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Biology Notes Form 1 – Biology Form 1 Notes – Form 1 Biology Notes
Introduction to Biology
Biology is a branch of science that deals with the study of living things. There are diverse forms of life
on earth ranging from the invisible microscopic living things to the gigantic life forms. It aims at
explaining the living world in terms of scientific principles.
It is important to note, however, that living
things interact with the non living things in the environment as Well. Biology, therefore also entails the
study of non living things as well.
The role of human beings in shaping the environment is also
investigated in biology.
In summary, biology deals with the study of origins, types, nature,
growth, development, interactions and maintenance of all life forms on earth.
Branches of Biology
Biology is such a broad field of knowledge. It is divided into two broad branches
1. Zoology– This is a branch of biology that deals with the study of animal life.
2. Botany– This is a branch of biology that deals with the study of plant life.
Within the two branches, there exist even smaller branches because the branches (botany and
Zoology) are very wide and complex.
The smaller branches of biology include:
a) Ecology– This is the study of the interrelationships between organisms and their
environment. Ecology aims at establishing how organisms are related to each other
and their environment.
Ecology is further subdivided into smaller branches. These
can be forest ecology, marine ecology, rangeland ecology etc.
b) Genetics– This sub-branch of biology deals with the study of inheritance and variation.
It deals with the study of how variations (differences) occur between parents and their
offspring. It is also concerned with how various characteristics are passed on from
parents to offspring.
c) Entomology– This is the study of insects.
d) Parasitology– This is the study of parasites.
e) Physiology– This deals with the study of the functions of various structures of an
organism. It deals with the processes that take place in the body of organisms.
f) Anatomy– The study of the internal structure of organisms
g) Microbiology– This is the study of microorganisms
h) Bacteriology– The study of bacteria
i) Ornithology– This is the study of birds
j) Itchthology-This is the study of fishes
This list is in-exhaustive as there are very many other branches of biology.
Importance of biology
benefit an individual in myriad ways. The study of biology is important in that:
environmental problems such as food shortage, poor health services, pollution and
environmental degradation.
veterinary medicine, animal husbandry, horticulture and dentistry.
life. These include skills of observing, identifying, recording, classifying, measuring,
analyzing and evaluating. These skills can enable one learn how to make right choices
and lead an improved life.
and how best these diseases can be prevented and cured.
international cooperation. Some biology related international conventions include:
> Joint development of HIV/AIDS vaccine by Kenyan and British scientists.
> The coordinated fight against Severe Acute Respiratory Syndrome involving scientist
all over the world.
> The fight to save the ozone layer from depletion through various international
agreements such as the Kyoto protocol.
> Management of resources through international treaties such as the CITES
(Convention against International Trade on Endangered Species).
Characteristics Of Living Things
Living things share a lot of characteristics in common. These characteristics are discussed below.
a) Nutrition
Nutrition is the process by which living things obtain and assimilate (utilize) nutrients.
Living things require nutrients for various purposes; growth, repair of worn out tissues and for
provision of energy. Plants manufacture their own food using light energy, carbon (IV) oxide,
water and mineral salts through the process of photosynthesis. Conversely, animals feed on
already manufactured foods from plants and other animals.
b) Respiration
Respiration is the process by which food substances are chemically broken down to release
energy. During respiration, oxygen is used while energy, carbon (IV) oxide and water are
released. Respiration occurs in all living cells.
The energy produced in living things is very
useful as it enables the living things carry out some of their physiological processes.
The energy
is also required for growth and development, movement and repair of worn out tissues.
c) Gaseous Exchange
Gaseous exchange refers to the process by which living things exchange oxygen and carbon
(IV) oxide across the respiratory surfaces. Animals always take in air rich in oxygen and give
out air rich in carbon (IV) oxide.
Carbon (IV) oxide is a waste product of chemical reactions in
the body. Animals require oxygen for respiration. Gaseous exchange, therefore, enables animals
obtain oxygen for respiration and get rid of carbon (IV) oxide, a waste product.
Plants, however, require carbon (IV) oxide for photosynthesis during the day. They give away
oxygen as a by-product. The plants equally require oxygen for respiration and give away carbon
(IV) oxide.
d) Excretion
This is the process by which living things separate and eliminate the waste or harmful
materials resulting from chemical reactions Within the cells. These harmful waste products of
metabolism maybe toxic to the body if they are left to accumulate in the cells of the living things
e) Growth and Development
Growth refers to an irreversible increase in size and mass while development refers to the
irreversible change in complexity of the structure of living things. Growth and development
of living things is essential as it enables the living things to attain maximum size that can enable
them to perform their functions and roles.
f) Reproduction
This is the process by which living things give rise to new individuals of the same kind. All
living things reproduce. Reproduction is essential as it leads to perpetuation of species and it
avoids extinction of certain animals and plants.
g) Irritability
This is the ability of living things to perceive (detect) changes in their environment and
respond to them appropriately. Living things respond to changes in temperature, humidity,
light, presence or absence of certain chemicals.
Response of organisms to these changes is
crucial as it enables them to escape from harmful stimuli. Ability to detect changes in the
environment also enables organisms to obtain resources in their environment.
h) Movement
Movement refers to change is position (displacement) of a part or parts of an organism.
Movement in plants includes folding of leaves, closing of flowers and growing of shoots towards
light. The change of position of an entire organism from one position to another is locomotion.
Study questions
a) Motor vehicles move, use energy and produce carbon dioxide and water. Similar
characteristics occur in living organisms yet motor vehicles are not classified as living.
List the other characteristics of living things that do NOT occur in motor vehicles.
b) Give the name to the study of:
Collection of Specimen
We have defined biology as the study of living things. For effective study, a biologist
may have to collect some living things or some parts of living things for observation and
analysis. The living things or parts of living things that are used for biological study are called
specimens.
Biological studies always take place in laboratories. A laboratory is a building or a
room that is designed and equipped for scientific studies.
Collections of living things especially animals may not be very easy. Some of the animals
are not easy to catch while some are quite dangerous. Knowledge on proper specimen collection and handling of is very important. We will discuss some of the apparatus used in specimen
collection.
a) Sweep net– This is used for catching flying insects.
b) Fish net– This is used for trapping small fish and other small Water animals.
c) Pooter– This is used for sucking small animals from rock surfaces or barks of trees.
d) Bait trap– This is used for attracting and trapping small animals including rats.
e) Pit fall trap– This is used for catching crawling animals.
f) Pair of forceps– This is an apparatus used for picking up small crawling animals e.g.
stinging insects.
g) Specimen bottles– These are bottles used for keeping collected specimen. They are of
different sizes depending on the size of the specimen being studied.
h) Magnifying lens– This is used to enlarge small objects. A hand lens is a common
magnifying lens used in the laboratory. The magnifying power of the hand lenses is
always indicated on the lens e. g. X10, X5, X8. The magnifying power of a lens shows
how many times the image will be enlarged compared to the object.
How to use a magnifying lens
To use a magnifying lens, place the object to be enlarged on the bench. Hold the magnifying lens
on one hand and while closing one eye, move the lens towards the object until the image comes
into clear focus.
If a magnifying lens is used to make a drawing of a specimen, the magnification of the drawing
will have no relation with the size of the drawing.
The magnification of the drawing can be calculated using the formula shown below.
Drawing magnification: Length of drawing divided by Length of the actual object
The sign of “times” must come before the magnification value e. g. X10, X5, X15 etc.
Precautions During Collection and Observation of Specimen
While collecting specimen for observation, a biologist should play close attention to the
following:
stinging plants or insects. Forceps and hand gloves should be used in such cases.
Comparison Between Plants and Animals
Plants
Animals
Chapter Two: Classification 1
Introduction
living things share similar characteristics discussed in the introductory chapter, the living
things exhibit a lot of differences.
In particular, animals and plants are all living things
yet they differ in many aspects. Amongst animals and plants also there exist a lot of
differences.
There are millions of different plant and animal types exhibiting a range of
differences. This created a need for a classification system of living things to make study
of the living organisms easier.
referred to as a taxon (plural: taxa).
evolutionary relationships (phylogeny) of the organisms. It is believed that all organisms
once had a common ancestor (theory of evolution). During classification, organisms that
are believed to have evolved along the same line of evolution are placed in one taxon.
taxonomy is a taxonomist.
observable features of organisms.
External features of plants used in classification
External features of animals used in classification
Importance of Classification
arranges the information on organisms in an orderly manner.
separate those with different features.
organisms
etc.
biology depend on classification of pests, disease vectors, pathogens and components of
an ecosystem.
Historical background of Classification
heavily relied on very few observable features. There was no standard classification
system as each and every scientist would classify organisms in a way that would suit his
intentions.
were also classified as herbs, trees, shrubs. Animals were also grouped into herbivores,
carnivores and omnivores.
a) Edible or non edible
b) Flowering or non-flowering
between living organisms. It has overcome the many weaknesses of the artificial
(traditional) classification systems.
changes that enabled them to live in different habitats. The structural changes account for
the great diversity of living organisms observed today.
contribution to the development of the modern classification system.
Taxonomic Units of Classification
placed as a matter of convenience.
are common in that group.
classification scheme.
first largest and highest group, the kingdom to the smallest and lowest unit, the species.
1. Kingdom
2. Phylum (animals)/division (plants)
3. Class
4. Order
5. Family
6. Genus
7. Species
All living organisms are classified into five major kingdoms:
a) Kingdom Monera– This is composed of microscopic unicellular organisms
mainly bacteria e.g amoeba.
b) Kingdom Protoctista– This kingdom is comprised of members who are
microscopic. Though, some are large enough to be seen with the naked eyes.
Members of this kingdom include algae and protozoa.
c) Kingdom Fungi– Members of this kingdom comprises the mushrooms, toadstools,
moulds and yeast.
d) Kingdom Plantae– This kingdom comprises the moss plant, ferns, maize plants,
hibiscus, meru oak tree etc.
e) Kingdom Animalia — Members of this kingdom include the tapeworms, hydra,
fishes, human beings, lizards, earthworms etc.
In hierarchy of classification, a kingdom is further divided into several phyla (plural of
phylum) or divisions (in plants). Within the phyla or divisions, organisms are further sorted out
into groups known as classes based on their similarities and mode of life.
Each class is further
subdivided into small groups called orders based on structural similarities. Orders subdivide into
families which subdivide into genera (plural for genus).
Genera are then subdivided into smaller
units of classification called the species.
Species is the smallest unit of classification whose members share many similarities and
can freely interbreed to give rise to fertile or viable offspring.
Members of a particular species can, however, exhibit various differences e. g. differences in skin
colour or body forms. Within the species, organisms can further be classified based on the
differences in colour or forms.
In humans, this gives the races, in animals the term used is breed
while in plants, variety is preferred. In bacteria, the term strain is used to describe the variant
forms.
Members of different but very closely related species can breed but the resulting
offspring will be sterile (infertile). In particular, a mule is a sterile offspring between a horse and
a donkey.
Moving from kingdom to species, it is important to note that the number of organisms
in each taxon decreases. The similarities, however, increase as one moves from kingdom to
species.
Scientific Naming of Living Organisms
naming system was developed by Carolus Linnaeus in the 18th century.
names by which the organisms are known in the vernacular languages. In particular, a cat
is an English name, mbura is a luo name, paka is a Swahili name etc. these names differ
across cultures and cannot be used by scientists to communicate across the world. This
makes sharing scientific knowledge on organisms very difficult. There was need for a
common language and this led to development of scientific language in latin.
widely spoken at that time. Similarly, latin language is a dead language hence not
subjected to a lot of changes. The scientific names are, therefore, static.
name adopts two names. This implies that the specific scientific name of an organism has
two names. This double naming system is known as binomial nomenclature.
which are internationally recognized and referred to as binomial nomenclature which
literally means the rule of double naming system.
Rules of Binomial Nomenclature
Binomial nomenclature requires that:
a) The first part of the scientific name is that of the genus name which should begin with a
capital letter. The second name is that of species. The species name should be written in
small letters e. g.
a) Maize- Zea mays
b) Lion- Panthera leo
c) Leopard- Panthera pardus
d) Domestic dog- Canisfamiliaris
e) Human being- Homo sapiens
b) When printed in books and other printed works, the scientific names should be printed in
italics. However, in handwritten manuscripts and typed works, the genus and species
names should be lined separately.
Printed work- Homo sapiens
c) The specific name is frequently written with the name of the scientist who first
adequately described and named the organism e. g. Balanus balanoides Linneaus.
d) Scientists must give a latinised name for a newly described animal or plant species where
a Latin name is missing e,g.
Aloe kilzfiensis– A type of aloe found in kilifi
Meladogyne kikuyuensis– A nematode found in kikuyu.
Origin of scientific names
Scientific names assigned to organisms can be:
Chapter Three: The Cell
Introduction
cells make up the structures of the living organisms and are responsible for carrying out
various biological processes in the bodies of the living organisms.
kingdom monera. These organisms are known as unicellular organisms.
and animals are multicellular.
instrument is required. The microscope is used to view the cells.
lenses for greater magnification.
lenses which provided a greater magnification. He used the microscope to view nuclei
and unicellular organisms including bacteria.
studies. Through this microscope, it was possible to study very finer details of structures.
The Light Microscope
on very fine details of the internal structures of cells.
is imperative to understand the parts and functions of various parts of a microscope.
magnification of the specimen.
by:
power is X8, then the total magnification of the specimen would be:
Magnification=Eyepiece magnification X Objective lens magnification
= 10 X 8
=X80.
Figure 1. The light microscope
Handling and Care of the Microscope
Part of the microscope: Limb
function: supports the body tube and stage
Base:
function: provides firm and steady support to the microscope
Body tube:
function: holds the eyepiece and the revolving nose piece
Coarse adjustment knob:
function: raises or lowers the body tube through longer distances to bring the image into sharper focus
Fine adjustment knob:
function: raises or lowers the body tube through smaller distances to bring the image into sharper focus. it is mostly used with the high power objective lens
Diaphragm:
function: an aperture that regulates the amount of light passing through the condenser to illuminate the specimen
Eye-piece:
function: contains a lens which contributes to the magnification of the specimen under review
Objective lens:
function: bring image into focus and magnifies it.
Mirror:
function: reflects light through the condenser to the object on the stage
Revolving nose piece:
function: holds the objective lenses in place and enables the change from one objective lens to the other
Condenser:
function: concentrates light on the object on stage
Stage:
function: flat platform where specimen on the slide is placed.it has two clips to hold the slide into position
The following rules should be observed when handling the microscope:
> Always use both hands when carrying the microscope. One hand should hold the base to
provide support while the other hand holds the limb.
> Never place the microscope too close to the edge of the working bench or table.
> Do not touch the mirror or the lenses with your fingers.
> Dirty lenses should be cleaned using a special soft lens tissue paper or tissue paper
moistened with ethanol. The other parts of the microscope may be cleaned using a
microscope.
> Do not wet any part of the microscope.
> Make sure the low power objective lens clicks into position in line with the eye piece
before and after use.
> After use, always clean and store the microscope in a safe place, free from moisture and
dust.
How to use the Microscope
ensure that maximum light can pass through. The circular area seen is referred to as the
field of view.
sufficient light is passing through the specimen.
comes into focus.
what you observe.
the focus using the coarse adjustment knob. For sharper images, use the fine adjustment
knob.
the fine adjustment knob to bring the details into sharper focus.
Cell Structures as seen under the Light Microscope
that can be observed under the light microscope include the cell wall, cell membrane,
cytoplasm, nucleus, vacuole and chloroplasts.
Figure 2 Plant and animal cells as seen under the light microscope
The cell as seen under the Electron Microscope
electrons to illuminate the specimen instead of light as in the case of light microscope.
between separate things which are close to each other.
in microbiology.
Figure 4. The plant cell
Structure and Functions of the Cell Organelles
Cell membrane
The three layers are composed of one layer of phospholipid sandwiched between two protein layers.
Cytoplasm
dissolved substances.
c) Mitochondrion
reactions that yield energy for the cell. Mitochondria is thus, referred to as the
powerhouse of the cell.
increase surface area for respiration.
requirements. Cells that require large amounts of energy contain high amount of
mitochondria.
> Mitochondria are self replicative that is they can divide to form new ones.
Figure 5. The Mitochondrion (Animal)
Figure 6, (generalize(lmage23 mitochondrion Structure)
throughout the cytoplasm.
referred to as rough or granular endoplasmic reticula. Endoplasmic reticula that are
not associated with ribosomes are called smooth endoplasmic reticula.
as enzymes. They also contribute to mechanical support.
e) Ribosomes
ribosomes are scattered within the cytoplasm (free ribosomes). Their largest dimension is
25 nanometres.
f) Lysosomes
enzvmes which break down large molecules. destroy Worn out oraanelles or even the
entire cells.
that might have been ingested in food. This explains their high relative abundance in
injured or infected cells.
out, they may destroy the whole cell.
g)Golgi bodies/Golgi apparatus
membrane.
1) They package and transport glycoproteins.
2) They are involved in secretion of synthesized proteins and carbohydrates.
3) They manufacture lysosomes.
Note: Golgi bodies are abundant in cells that are active in secretion. For instance pancreatic cells
which secrete enzymes and the nerve cells which secrete neurotransmitter substances.
h)Centrioles
organisms.
i) Chloroplasts
like stroma through which runs a system of membranes that are stacked together to form
grana.
photosynthesis.
j) Vacuoles
contain one large centrally placed vacuole.
the cell. This influences how materials move in and out of the cell.
the contractile vacuole excretes unwanted materials from the cell.
k) Cell wall
1. It gives plant cells their definite shape
2. It provides mechanical support and protection against mechanical injury.
3. The cell wall allows gases, water and other substances to pass through it.
i) Nucleus
nucleoplasm in which nucleolus and chromatin materials are suspended. The nuclear
membrane has minute pores, nuclear pores which allow materials to move in and out of
the nucleus.
hereditary materials.
Comparison between Plant Cells and Animal Cells
While there exist many similarities between plant and animal cells, there are a number of
differences.
Plant cells
Animal cells
Estimation of Cell Size
The light microscope can be used to estimate the size of a cell. Most cells have diameters
smaller than a millimeter. Due to this, cell sizes are always measures in smaller units.
These are micrometres and nanometers. These units of measurements are related as
shown below.
1 millimeter (mm) = 1000 micrometres (pm).
1 micrometer (pm) = 1000 nanometres (nm).
Procedure in cell size estimation
of cells.
microscope.
the first mark and the last one across the field of view. Count only the spaces between
two thick dark lines.
cell diameter = diameter of the field of view in micrometers divided by number of cells.
Cell Specialization. Tissues. Organs and Organ Systems
Cell Specialization/Cell Differentiation
specific functions
has a tail-like extension for swimming towards the ovum.
Tissues
same function.
a) Tissue types in animals
1. Epithelial tissue– This is a thin continuous layer of cells for lining and protection of
internal and external surfaces.
2. Skeletal muscle– This is a bundle or sheets of elongated cells with fibres that can
contract. Its contraction and relaxation brings about movement.
4. Blood tissue– This is a fluid containing red blood cells, white blood cells and platelets.
The main functions of blood tissue are transportation of nutrients and gases as well as
protection of the body against infections.
5. Connective tissue– This tissue consists of strong fibres that connects other tissues and
organs thereby holding them in position.
b)Tissue types in plants
1. Epidermal tissue– This is a single thin layer of cells covering the outer surfaces. It
protects inner tissues of plants from mechanical damage and infection.
2. Palisade tissue– This is a group of cells rich in chloroplasts containing chlorophyll. It has
a site for the absorption of light energy and manufacture of food by photosynthesis.
3. Parenchyma tissue– This tissue consists of special thin walled irregularly shaped cells.
They form packaging and storage cells.
4.Conducting tissue/Vascular bundle– This tissue consists of xylem and phloem. Xylem
conducts water and dissolved mineral salts in a plant while phloem conducts food
substances in solution.
Organs
function.
a) Heart– composed of connective, muscle, epithelial and blood tissues.
b) Kidney– Composed of connective, epithelial and muscle tissues
c) Brain– Composed of epithelial, connective tissues
d) Lungs– Composed of epithelial, connective tissues.
a) Roots– composed of epidermal, conducting and parenchyma tissues.
b) Flowers– This is composed of epidermal, conducting tissues.
c) Stem– Composed of conducting, parenchyma, and epidermal tissues and palisade
tissues in some cases
d) Leaves– Composed of palisade, conducting and epidermal tissues.
Organ system
This is a group of organs Whose functions are coordinated and synchronized to perform
the same function.
Organ systems are more pronounced in animals than in plants
Organ systems in animals include
a) Digestive system composed of organs such as oesophagus, stomach, intestines and
their associated glands.
b) Circulatory system composed of the heart, blood vessels (arteries, veins, capillaries).
c) Excretory this is composed of kidney, liver, and blood vessels.
d) Respiratory system composed of trachea, bronchus, and lungs.
e) Reproductive system composed of the reproductive organs and associated glands.
f) Nervous systems composed of the brain, spinal cord, eye, ear organs.
Chapter Four: Cell Physiology
Introduction
activities of life or of living matter such as organs, tissues or cells. It aims at
understanding the mechanism of living.
the body cells of organisms.
perform various functions of life. In particular:
a) Chloroplasts play a vital role in carbohydrate synthesis.
b) Mitochondrion produces energy required to carry out life processes.
c) Ribosomes manufacture of proteins.
into the chloroplasts.
oxygen have to be taken into the mitochondrion. Energy, carbon (IV) oxide, water and
alcohol (in plants) are some of the end products of respiration.
harmful when allowed to accumulate in the cells. They, thus, have to be eliminated from
the cells.
organelles where these physiological processes are taking place. There is a constant
movement of materials across the cell membrane in the cells.
which materials move in and out of the cells.
Structure of the membrane
membrane and chloroplast membrane.
materials in and out of the cells.
(it is a lipoprotein layer) the overall thickness of the cell membrane is about 7.5 nm thick.
out of the cells.
Properties of the cell membrane
a) The cell membrane is semi permeable– The pores that occur on the cell membrane
allows the passage of the small size molecules but does not allow the passage of the large
sized molecules.
Such a membrane is said to be selectively permeable or semi-permeable.
In particular, when a cell is surrounded by a dilute sugar solution, the small sized water
molecules will enter the cell but the larger sugar molecules will not pass through the cell
membrane.
In contrast, the cell wall is permeable as it allows both sugar and water
molecules to pass through it; it has larger pores. This property of selectively permeability
enables the cell membrane to select what enters and leaves the cell.
b)The cell membrane is sensitive to changes in temperature and pH– Cell membranes
are made up of protein. Proteins are adversely affected by extreme changes in
temperature and pH.
Changes in temperature and pH will alter the structure of the cell
membrane thereby hindering the normal functioning of the cell membrane. High
temperature denatures (destroys) the proteins thereby impairing the functions of the cell
membrane.
c)The cell membrane possesses electric charges– The cell membrane has both positive
and negative charges. These charges affect the manner in which substances move in and
out of the ells. The charges also enable the cell to detect changes in the environment.
Physiological Processes of the Cell membrane
move in and out of the cells across the cell membrane.
a) Diffusion
b) Osmosis
c) Active transport
Diffusion
to another randomly. This movement of gas or liquid particles is observed to be from
regions of high concentration to a region of low concentration. The process by which
particles move from a region of high concentration to a region of low concentration
is known as diffusion.
of the flower scent particles or perfume particles move from a region of high
concentration.
particles.
region of low concentration is known as the diffusion gradient/concentration gradient.
Demonstration of the process of diffusion using_potassium manganate (VII)
Requirements: potassium manganate (VII) crystals, glass tubing, 100 cm3 beaker and water.
Procedure
a) Hold the glass tubing vertically in a beaker so that one end of the tubing rests on the
bottom of the beaker.
b) Cautiously and quickly drop a crystal of potassium manganate (VII) through the upper
opening of the glass tubing.
c) Close the upper hand of the glass tubing with the thumb.
d) Half fill the beaker with water.
e) Carefully withdraw vertically the glass tubing so that the crystal is left undisturbed at the
bottom of the beaker.
f) Record your observations for the first 15 minutes.
g) Explain your observations.
Expected observations
the water and eventually all the water turned purple.
Explanation
manganate (VII) particles. The potassium manganate (VII) particles break away from the
crystals, dissolve in water and then diffuse through the water until they are evenly
distributed.
The Role of Diffusion in Living Organisms
a) In Plants
Diffusion plays an important role in plants in that:
water. For those salts whose concentration in soil water is higher that their concentration
in the cell sap of root hair cells, they move into the root hair cells through diffusion.
Plants require mineral salts for numerous life processes.
carbon (IV) oxide) diffuse across the stomata and lenticels of plants.
leaves to other parts of the plant.
b) In Animals
In animals diffusion plays the following important roles
of digestion such as amino acids and glucose diffuse across the wall of the ileum into the
blood for transport to other parts of the animal body.
gaseous exchange occurs at certain structures known as respiratory surfaces.
These
include the skin, gills, lungs, tracheal system and the cell membrane (in unicellular
organisms). Gaseous exchange at these surfaces occurs through the process of diffusion.
animals.
Factors affecting the rate of Diffusion
a) Diffusion gradient
the concentration of diffusing molecules also increases diffusion gradient with
corresponding regions hence increases the rate of diffusion.
b) Surface area to volume ratio
surface area to volume ratio, the greater the rate of diffusion will be. Conversely, low
surface area to volume ratio results in a low diffusion rate.
This is because the small organisms have a large surface area to volume ratio. As a result,
most of their body parts are closer to the external surrounding leading to faster diffusion.
foods, respiratory gases and waste products.
excretion. They have an additional transport system.
animals lose a lot of heat to the surrounding compared to the large animals.
c) Thickness of membranes and tissues
distance covered by the diffusing molecules is greater through the thicker membranes.
d) Size of molecules
e)Temperature
causing them to move faster, this implies that the rate of diffusion increases with increase
in temperature.
Osmosis
concentration (dilute solution) to a region of low concentration (concentrated solution)
through a semi permeable membrane.
solvent (Water) particles from a region of high concentration to a region of low
concentration.
Demonstration of Osmosis Using a Visking Tubing
Requirements
5OOcm3 beaker, visking tubing, a piece of thread, glass rod, concentrated sugar solution, 500 cm3
distilled Water.
Procedure
1. Into the beaker, put 350 cm3 of the distilled water.
2. Dip the visking tubing in water to moisten it. Open the visking tubing and tie one end
with the thread provided.
3. Half fill the visking tubing with the sugar solution provided and then tie the open end of
the tubing. Ensure no sugar solution spills out of the tubing.
4. Immerse the visking tubing into the distilled water in the beaker and suspend it using the
glass rod provided.
5. Leave the set up for about 30 minutes.
6. Record your observations.
7.Explain the observations made.
Observations
amount of water in the beaker decreased. This implies that water moved from the beaker
into the visking tubing.
Explanation
higher concentration of water molecules than the visking tubing. The water molecules
diffused from the beaker (where they are highly concentrated) into the visking tubing
(where they are lowly concentrated).
Even though there is a higher concentration of sugar
molecules in the visking tubing, they were not able to diffuse out of the visking tubing
due to their large molecular sizes. The visking tubing is semi permeable.
membranes that can be used in this experiment.
Osmosis explained
movement of water molecules from their region of high concentration (dilute solution) to
a region of low concentration (the highly concentrated solution) across the semi
permeable membrane. The semi permeable membrane does not allow movement of solute
particles across it.
same concentrations.
are said to be isotonic to each other.
hypotonic solution has less of the solute molecules but more of the solvent molecules.
particles is referred to as a hypertonic solution.
net movement of solvent molecules to any of the solutions since they have the same
concentration of solvent molecules.
Osmotic pressure
membrane, the concentrated solution will develop a force with which it draws water
through the semi permeable membrane from the distilled water.
itself.
Osmotic potential
from pure water when separated by a semi permeable membrane.
Water Relations in Animals
happen if an animal cell say red blood cell is placed in solutions of varying
concentrations
a) Red blood cell in hypotonic solution e. g. distilled water
cell cytoplasm.
When a red blood cell is placed in a hypotonic solution, water will move
into the cell through osmosis. The cell will swell and burst. Swelling of red blood cell
when placed in a hypotonic solution is referred to as haemolysis. The cell is said to be haemolysed.
b) Red blood cell in hypertonic solution
blood cell cytoplasm.
Water will, therefore, be drawn out of the cell into the hypertonic
solution. The cell will shrink and become small. The cell is said to be crenated.
The
process by which animal cells shrink and become smaller when placed in hypertonic
solutions is referred to as crenation.
c) Red blood cell in isotonic solution
When placed in an isotonic solution, the cell remains unchanged. This is because there
will be no net inflow or outflow of water between the cell and the solution.
Note:
that the body fluids and blood plasma surrounding the cells must be kept at the same
concentration as the animal cells.
This will prevent bursting or shrinking of the cells that
would otherwise impair their physiology.
same concentration.
Water Relations in Plants
contains vacuole with sap. The sap is a solution of salts and sugars and is bound by a
membrane, the tonoplast.
permeable.
a) Plant cell in hvpotonic solution e. g. distilled water
hypotonic solution through osmosis causing the cell to distend.
animal cells.
pressure on the cell wall called turgor pressure.
stretch until the cell cannot stretch any more. The cell becomes firm and is said to be
turgid.
it gains more water through osmosis.
pressure to stretching that is equal and opposite to turgor pressure called wall pressure.
b) A glam cell in a hygertonic solution
through osmosis. As the water moves out of the cell, the cell starts to shrink, becomes
less rigid or flabby and is said to be flaccid.
away from the cell wall towards the centre. The process through which plant cells lose
water, shrink and become flaccid is called plasmolysis.
called deplasmolysis.
Wilting
from the soil making the plant cells to lose their turgor pressure and droop.
through evapotranspiration is significantly reduced.
wilting and instead undergo permanent wilting.
Role of Osmosis in Organisms
soil through osmosis. Osmosis also helps in distribution and movement of water from the
roots to other parts of the plant.
When the cells of these plants take in water through osmosis, the cells become firm or
rigid and thus gain support.
surrounding the stomata synthesize glucose through photosynthesis in the presence of
light.
As glucose accumulates in the guard cells, the osmotic pressure of the guard cells
increase making them to draw water from adjacent cells through osmosis. When the
guard cells become turgid, they bulge outwards leading to opening of the stomata.
Opening of the stomata is crucial as it allows for gaseous exchange in plants. At night,
there is no glucose synthesis.
The glucose available in the guard cells is respired on
leading to reduction of glucose and consequently reduction in osmotic pressure. The
guard cells lose turgidity and close the stomata.
nitrogen deficient soils and trap insects from whence they obtain the nutrients. These
plants possess special structures that suddenly change their turgor pressure when
disturbed.
The change in turgor pressure enables the special structures to rapidly close
thereby trapping the insects.
through osmosis through the tubular walls. This enables animals to maintain the osmotic
pressure of the body fluids.
Factors Affecting the Rate of Osmosis
separated solutions have a greater difference in osmotic pressure. In summary, the greater
the concentration gradient, the greater the rate of osmosis and vice versa.
increases the energy content of the molecules.
while the rate of osmosis is greater through thinner membranes.
Active Transport
membrane and against a concentration gradient.
cells. In particular, there are some mineral salts that occur at low concentrations in the
soil water than in the cell sap.
Some of these mineral salts cannot be absorbed by the
plants through diffusion. A mechanism that would move them into the cells against the
concentration gradient will be useful.
on concentration gradient for them to take place.
the moving these substances across the membrane. These carrier molecules combine with
the substances being transported across the membrane and then move them from one side
of the membrane to the other side.
Role of active transport in living organisms
and saline environments
Factors affecting the rate of Active Transport
production process in living cells.
a) Oxygen concentration
Oxygen is required in respiration process that yields energy for active transport. Under low
oxygen concentration, the rate of respiration will be low hence there will be production of little
energy leading to low rate of active transport. Increase in oxygen concentration translates into a
higher energy production leading to high rate of active transport.
b) Change in pH
Change in pH affects the respiratory process which is enzyme controlled. Respiratory enzymes
require optimum pH for their efficient activity. Extreme pH conditions will increase lower the
rate of active transport since the enzymes controlling respiration Will be denatured.
c) Glucose concentration
Glucose is the chief respiratory substrate. At low glucose concentration, there will b less
production of energy leading to decreased rate of active transport. Rate of active transport
increases with increase in glucose concentration due to increase in the rate of energy production.
d ) Temperature
Temperature affects the enzyme controlled respiration process. At low temperatures, the
enzymes are inactive hence the rate of respiration will be low resulting into low rate of active
transport since there will be less production of energy. An increase in temperature increases the
rate of respiration since the enzymes become more activated. At temperatures beyond 40 degrees
celcius, the enzymes become denatured, respiration stops and so does active transport.
e) Presence of metabolic inhibitors e. g. cyanide.
These are substances which act as metabolic poisons. They stop the rate of respiration leading to
production of no energy. Active transport is, thus, stopped.
Nutrition Plants And Animals
Introduction
nutrients. It is one of the fundamental characteristics of living things.
The nutrients obtained are useful to the living organisms in many ways:
a) The nutrients are required for growth and development of the living organisms.
b) The nutrients are required for energy provision as they are broken down to release
energy.
c) They nutrients are also required for repair of worn out tissues
d) Nutrients are required for synthesis of very vital macromolecules in the body such as
hormones and enzymes.
Modes of nutrition
There are two main nutrition modes:
a) Autotrophism mode of nutrition through which living organisms manufacture their own
food from simple inorganic substances in the environment such as carbon (IV) oxide,
water and mineral ions. Organisms that make their own food through this mode are
autotrophs.
b) Heterotrophism mode of nutrition in which living organisms depend on already
manufactured food materials from other living organisms. Heterotrophs are the organisms
that feed on already manufactured food materials.
Autotrophism
In this mode of nutrition, organisms manufacture their own food from readily available
materials in the environment. These organisms use energy to combine carbon (IV) oxide,
water and mineral salts in complex reactions to manufacture food substances. Depending
on the source of energy used to manufacture the food, there are two types of
autotrophism:
a)Chemosynthesis
This is the process whereby some organisms utilize energy derived from chemical
reactions in their bodies to manufacture food from simple substances in the environment.
This nutrition mode is common in non green plants and some bacteria which lack the sun
trapping chlorophyll molecule.
b) Photosynthesis
the environment such as carbon (IV) oxide and water using sunlight energy.
and bacteria are also photosynthetic.
Importance of Photosynthesis
1. Photosynthesis helps in regulation of carbon (IV) oxide and oxygen gases in the
environment.
2. Photosynthesis enables autotrophs make their own food, thus, meet their nutritional
requirements.
3. Photosynthesis converts sunlight energy into a form (chemical energy) that can be
utilized by other organisms that are unable to manufacture their own food.
is important to understand the leaf structure.
External leaf structure
lamina- the broad flat surface, margin- the outline and the leaf apex.
leaves with some leaves reduced to needle like shape.
This helps reduce the rate of water
loss in such plants. However, the plants in areas of water abundance have broad leaves to
enable them lose the excess Water.
a) Cuticle
lower leaf surfaces.
Functions of the cuticle
a) Being waterproof, it minimizes water loss from the leaf cells to the environment through
transpiration and evaporation.
b) It protects the inner leaf tissues from mechanical damage.
c) It prevents entry of pathogenic microorganisms into the leaf.
b) Epidermis
are flattened and lack chloroplasts.
Functions of the epidermis:
a) It protects the leaf from mechanical damage.
b) It also protects the leaf from entry of disease-causing microorganisms.
c) It secretes the cuticle.
which exchange of materials occur. The opening and closing of the stomata is controlled
by the guard cells. Each stoma is controlled by two guard cells.
and thinner outer cell wall.
Adaptations of the guard cells
osmosis from the neighboring cells making them to open the stomata.
guard cells. As they draw water through osmosis, they bulge making the stomata to open.
c) Palisade mesophyll
sunlight for photosynthesis.
greener than the lower surfaces.
d) Spongy mesophyll layer
the cells which permits free circulation of gases carbon (IV) oxide and oxygen into the
photosynthetic cells. Spongy mesophyll cells contain fewer chloroplasts compared to
palisade cells.
e) Vascular bundle/tissue
tissues. Xylem tissues conduct Water and some dissolved mineral salts from the roots to
other plant parts while phloem translocates manufactured food materials from
photosynthetic areas to other plant parts.
Chloroplast
membrane bound organelle.
called stroma.
are contained in the grana.
place.
Adaptations of the leaf to photosynthesis
and for gaseous exchange.
molecules which trap sunlight energy for photosynthesis.
absorption of sunlight energy.
the photosynthetic cells and phloem to translocate manufactured food materials to other
plant parts.
Raw materials for photosynthesis
Conditions for photosynthesis
Photosynthesis Process
summarized into two main reactions.
a)Light reaction/Light stage
cannot take place.
i) Photolysis of water
and oxygen gas.
energy for photolysis.
plant for respiration.
Water– Hydrogen atoms + Oxygen gas
ii) Formation of adenosine triphosphate (ATP)
plant tissues with a phosphate molecule to form Adenosine Triphosphate (ATP). ATP is
an energy rich molecule that stores energy for use in the dark stage when sunlight energy
could be unavailable.
ADP + P = ATP
b) Dark reaction/Dark stage
from the ATP formed during light stage.
(IV) oxide molecule with hydrogen ions to form a simple carbohydrate and a water
molecule.
synthesis reactions.
inactive. When a lot of simple sugars accumulate in the chloroplasts, osmotic pressure of
the guard cells would increase causing the guard cells to draw a lot of water through
osmosis. This makes the guard cells to bulge and open the stomata. This can result into
excessive water loss.
photosynthesis has taken place in a leaf, therefore, a test for presence of starch and not
simple sugars is carried out.
Testing for starch in a leaf
Requirements
Procedure
that the leaf has photosynthesized.
enzymes and stops any chemical reactions in the leaf.
boil in a water bath. Methylated spirit is highly flammable hence should be boiled
indirectly. Boiling with methylated spirit or alcohol decolourises the leaf (removes the
chlorophyll). This ensures that the leaf becomes white so that colour changes can be
observed easily when iodine is added.
leaf.
Observations
Factors affecting the rate of photosynthesis
a) Carbon (IV) oxide concentration
0.03%, an increase in carbon (IV) oxide concentration translates into an increase in the
rate of photosynthesis up to a certain point when the rate of photosynthesis becomes
constant.
At this point, other factors such as light intensity, water and temperature
become limiting factors.
b)Light intensity
level. Beyond the optimum light intensity the rate of photosynthesis becomes constant.
To this effect, plants photosynthesize faster on bright and sunny days than on dull cloudy
days.
and blue wavelengths of light for photosynthesis. Light duration also affects
photosynthesis rate.
c)Temperature
photosynthesis is slow because the enzymes are inactive. As temperature increases, the
rate of photosynthesis increases because the enzymes become more active.
Rate of
photosynthesis is optimum at (35-40) °C. Beyond 40°C the rate of photosynthesis
decreases and eventually stops since the enzymes become denatured.
d) Water
photosynthesis will be severely affected.
Experiment to investigate the gas produced during photosynthesis
Requirements
wooden blocks, test tubes, wooden splints and sodium hydrogen carbonate.
Procedure
a) Set up the apparatus as shown in the figure below
b) Place the set up in the sunlight to allow photosynthesis to take place.
c) Leave the set up in the sun until sufficient gas has collected in the test tube.
d) Test the gas collected with a glowing splint.
e) Record your observations.
Note:
of carbon (IV) oxide in the water since water has a low concentration of carbon (IV)
oxide.
the low light intensity in water where terrestrial plants cannot easily photosynthesize.
photosynthesis:
1) Carbon (IV) oxide concentration: Carry out the experiment using different
amounts of dissolved sodium hydrogen carbonate e. g 5 g, 10g, 15g, 20g and
examine the rate at which the gas collects.
2) Light intensity: An artificial light source can be used. Illuminate the plant and
vary the distance between the set up and the light source While recording the time
it takes for the gas jar to fill or counting the number of bubbles peer unit time.
3) Temperature: carry out the experiment at varying temperatures and record the
rate at which the gas collects.
Experiments on factors necessary for photosynthesis
Light
Requirements
boiling tube, light proof material e.g. aluminium foil, potted plant and clips.
Procedure
to ensure that all the starch in it is used up. This makes the leaves ideal for investigating
whether starch would form in the experimental period. This is called destarching).
leaves and one that was not covered.
Carbon (IV) oxide
Requirements
Procedure
Chlorophyll
lack chlorophyll.
place in them.
Procedure
Chemicals Of Life
and their reactions.
Carbohydrates
Monosaccharides
Properties of Monosaccharides
Benedict’s solution to red brown copper (I) oxide when heated.
Note:
a process known as condensation. Water molecules are produced in the process.
Functions
body.
Disaccharides
condensation.
is called glycosidic bond.
transported in plants
Properties of Disaccharides
as a complex reducing sugar.
Hydrolysis is the process through which complex molecules are broken down in the
presence of water molecules.
hydrolysis can be carried out by boiling the disaccharide in dilute aid such as
hydrochloric acid.
Functions
and inert nature.
Polysaccharides
condensation.
Properties of polysaccharides
Examples of polysaccharides
a) Starch– Made by linking numerous glucose molecules. It is a form in which
carbohydrates are stored in plants.
b) Glycogen– Is a storage carbohydrate in liver and muscles of animals. It is broken down to
glucose in animals when blood glucose falls.
c) Cellulose– This is a structural polysaccharide in plants. It is a component of the cell wall
d) Chitin– A structural carbohydrate found in cell wall of fungi and arthropod exoskeletons
Functions of polysaccharides
storing carbohydrates.
Lipids
oxygen but higher hydrogen compared to carbohydrates.
three fatty acids and a glycerol molecule are linked through a condensation reaction.
type of fatty acids that link up with the glycerol.
also form through condensation.
Properties of lipids
form emulsions
Functions
carbohydrates when oxidized per unit weight. However, they are less preferred as source
of energy because they require a lot of oxygen to oxidize. In addition, they are insoluble
hence not easy to transport to respiratory sites.
This explains why some desert animals such as camels store large quantities of fat in their
bodies.
shock absorbers.
conductors of heat hence do not conduct heat away from the body. Organisms in cold
areas tend to be short and plump as they have fatter fat adipose.
Proteins
nitrogen and sometimes phosphorous or sulphur or both.
Some proteins molecules contain other elements. In particular, haemoglobin contains
iron.
acids are of two kinds:
a) Essential– These are those amino acids that cannot be synthesized by the body
systems hence have to be supplied in the diet.
b) Non essential– These are amino acids that can be synthesized by the body
mechanisms hence do not need to be supplied in the diet.
group. Amino acids differ from each other by the alkyl group.
a) First class proteins– Contain all essential amino acids
b) Second class proteins– Proteins lack one or more essential amino acids
Protein synthesis
Several amino acids link up to form a polypeptide chain. Proteins are made up of long
chain polypeptides.
sequence in which the amino acids link up in the polypeptide chain.
Properties of Proteins
suspended in water.
organic solvents also denature proteins.
conjugated proteins such as:
Functions of proteins
a) They are structural compounds of the body. Cell membrane is protein in nature. Hair,
nails and hooves are made up of protein keratin.
b) Proteins are broken down to release energy during starvation when all carbohydrate and
lipid reserves are depleted.
c) Functional proteins play vital roles in metabolic regulation. Hormones are chemical
messengers while enzymes regulate the speed of metabolic reactions.
d) Proteins such as antibodies provide protection to the body against infections
e) Some protein molecules are transport molecules. Haemoglobin molecule plays a crucial
role in transportation of respiratory gases.
f) Proteins play a vital role in blood clotting e. g. fibrinogen.
g) Contractile proteins such as actin and myosin bring about movement.
Enzymes
What are enzymes?
Types of enzymes
a) Extracellular: Are produced within the cells but used outside the cells e. g. digestive
enzymes.
b) Intracellular: Are enzymes produced and used within the cells e. g. respiratory enzymes.
Importance of Enzymes
life.
DNA.
utilized by the cells.
poisonous substances less harmful.
Enzyme nomenclature
a).Trivial naming
Examples
b). Use of suffix -ase
or by adding the suffix to the reaction being catalyzed by the enzyme.
Substrates
Processes/Reactions
Hydrolysis ……………….. ..hydrolase
Reduction ………………… ..reductase
Oxidation …………………. ..oxidase
Mechanism of action of Enzymes
which the substrate molecules bind to the enzymes. The reaction is then catalyzed and the
end products released. The enzyme is free to bind with another substrate molecule. The
enzymes can be used again and again.
Properties of Enzymes
Factors affecting enzyme activity
a)Temperature
collisions leading to low enzyme activity.
increases leading to increased collisions hence increase in enzyme activity.
enzymes get denatured and their active sites get destroyed.
b)pH
under acidic conditions e. g. pepsin. However, most intracellular enzymes work better
under neutral conditions.
c)Enzyme Specificity
particular reaction.
d)Substrate Concentration
activity is low.
sites of the enzymes will be occupied and there will also be an increase in enzyme-
substrate collisions leading to increased reaction.
sites are utilized. The enzymes become the limiting factor of reaction. Increasing enzyme
concentration would increase the rate of enzyme activity.
e) Enzyme Concentration
beyond which the rate of reaction becomes constant.
and also fewer enzyme-substrate collisions that would lead to reactions.
increase in number of active sites and enzyme-substrate collisions.
Increasing substrate concentration increases the rate of reaction.
f) Enzyme co-factors
as vitamins.
reactions.
g) Co-enzymes
functioning. Some enzymes will not function without them.
Examples
NAD- Nicotine Adenine Dinucleotide.
FAD- Flavine Adenine Dinucleotide.
NADP- Nicotine Adenine Dinucleotide Phosphate.
h) Enzyme inhibitors
1. Competitive
2. Non- competitive
Competitive inhibitors
up the shape of the substrates and compete for the active sites of the enzymes.
site for a long time) thereby slowing down the rate of enzyme activity.
Non competitive inhibitors
the enzyme at any site other the active site and alter the structure of the active site of the
enzyme. The normal substrate, therefore, fails to bind to the active site leading to
decreased rate of reaction.
Examples of non competitive inhibitors
Heavy metals (such as lead, mercury, silver), Cyanide, organophosphates such as malathion.
Heterotrophism
food substances such as carbohydrates, proteins and lipids.
food substances that can be absorbed and be utilized by the cells.
Modes of Heterotrophism
substances.
decomposition.
nutrients on another organism, the host.
mutually benefit from each other.
a) Parasitism
hosts and damage their tissues thereby weakening them.
b) Symbiosis
> Rhizobium and leguminous plants: rhizobium fixes nitrogen for the legume while
the bacteria obtains manufactured food from the legumes.
> Lichen: association of fungi (absorbing water and nutrients) and algae
(manufacturing food for the association.
> Catalase digesting bacteria and ruminants.
Dentition
utilized by the cells. The breakdown is both physical and chemical.
substances.
Types of Dentition
the same size and shape. Fishes and birds have homodont dentition.
incisors, canines, premolars and molars. Heterodont dentition is common with mammals
and reptiles.
a) Incisors
a. Canines
carnivores.
b. Premolar and molar
Classes of Holozoic Heterotrophs
a) Herbivores: heterotrophs that exclusively feed on vegetation.
b) Carnivores: heterotrophs exclusively feed on flesh.
c) Omnivores: heterotrophs that feed on both flesh and vegetation.
Dental Formula
a) i-incisors.
b) c-canines.
c) pm-premolars.
d) m-molars.
premolars and four molars on the upper jaw. On the lower jaw, it had eight incisors, no
canines, six premolars and six molars.
a) Write down its dental formula.
b) State its mode of feeding.
c) Give a reason.
Herbivores
pressed and cut by the lower incisors.
which allows the tongue to manipulate food.
out surfaces due to grinding.
grinding of grass.
Carnivores
carnassial teeth which have smooth sides and sharp edges to slice through flesh and crush
bones
Dental Diseases
a) Dental Carries
of vitamin D, lack of cleaning teeth and general ill-health. The bacteria in the mouth
break down the sugars to form energy and organic acids. The acids corrode the enamel.
b) Periodontal Diseases
of gums.
than children.
Are of two types:
a) Gingivitis– Characterized by reddening of gums, bleeding and pus in the gums.
b) Pyorrhea– The teeth become loose due to infection of the fibres holding the teeth in
the sockets.
Dental Hygiene
Digestion
chemically into simpler food substances that can be absorbed by body cells.
absorbed into the bloodstream without undergoing digestion.
bladder, salivary glands.
Digestion in the mouth
process is called mastication.
action.
from the salivary glands. The salivary glands are:
a) Sublingual salivary gland; beneath the tongue
b) Sub mandibular gland: under the jaw
c) Parotid gland: Found in the cheeks in front of the ears.
then pushed to the back of the mouth to initiate the swallowing process. The boluses are
then moved to the stomach via oesophagus. Movement is facilitated by a wave of
muscular contractions of longitudinal and circular muscles of the oesophagus known as
peristalsis.
swallowing.
Digestion in the stomach
the stomach via the cardiac sphincter (a muscular valve).
produce movements that mix the contents of the stomach. The mixing process is known
as churning and results in formation of a fluid called chyme
stimulates the gastric glands in the stomach walls to secrete gastric juice which contains:
a) Pepsinogen-This is activated to pepsin which breaks down proteins to peptides.
b) Rennin– Digests caseinogens protein in milk to casein (curd).
e) Hydrochloric acid– This:
d) Mucus– Forms a protective barrier to the stomach wall against corrosion by the
HC1. Mucus is secreted by goblet cells in the epithelial membrane of the
alimentary canal.
Duodenum
chyme is let down into the duodenum in small quantities.
a) Gall bladder in the liver- Secretes bile.
b) Pancreas- Secrete hormones and digestive enzymes.
i. Secretin hormone from the pancreas: Secretin stimulates secretion of pancreatic
juice into the duodenum
ii. Cholecystokinin from the duodenal wall: This stimulates secretion of bile from
the gall bladder.
a) Pancreatic amylase– This facilitates breakdown of the remaining starch into maltose
b) Trypsin– Digests proteins into peptides.
c) Pancreatic juice-Digests lipids into fatty acids and glycerol
d) Sodium hydrogen carbonate– This:
Provides alkaline medium for activity of the duodenum enzymes.
taurocholate. These salts:
i. Aid in emulsification (breakdown of fat molecules into tiny fat droplets to
increase surface area for digestion).
ii. The salts also provide a suitable alkaline medium for action of the duodenal
enzymes.
iii. In addition they neutralize the acidic chyme.
Digestion in the ileum
an alkaline fluid known as succus entericus (intestinal juice). The arrival of chyme in
ileum stimulates secretion of intestinal juice which contains:
a) Maltase: speeds up breakdown of maltose to glucose
b) Sucrase: speeds breakdown of sucrose to glucose and fructose
c) Peptidase: speeds breakdown of peptides to amino acids
d) Lipase: speeds breakdown of lipids to fatty acids and glycerol.
e) Lactase: speeds breakdown of lactose to glucose and galactose.
f) Polypeptidase: speeds breakdown of plypeptides into amino acids
Note:
The mucus secreted by the goblet cells lubricates food along the alimentary canal and
also protect the canal from being digested by enzymes.
At the end of digestion in the ileum, the resulting watery emulsion is called chyle; it
contains soluble end products of digestion ready to be absorbed.
Absorption
cellular lining of the villi.
are absorbed at the stomach. Alcohol is equally absorbed here without undergoing
digestion.
walls into the blood system by active transport.
transported to the liver before they are circulated to other body parts.
vessels. The lymphatic vessels later join the blood circulatory system which transports
them to other body parts.
a) It is long to provide a large surface area for absorption
b) It has a narrow lumen so as to bring the digested food into close contact with the
walls of the ileum for easier absorption
c) It is highly coiled to slow down movement of food thus allowing more time for
digestion and absorption of food.
d) The inner surfaces have numerous villi and microvilli to increase surface area for
absorption of end products of digestion.
e) The epithelial lining is one cell thick to reduce the distance through which
digested food diffuses.
f) Has a dense network of blood capillaries into which digested food materials
diffuse to increase transport and thus maintain a steep concentration gradient.
g) Have lacteal vessels in the villi for absorption of fatty acids and glycerol.
Egestion
> This is the process through which the undigested and indigestible food substances are
eliminated from the body.
Caecum and Appendix
herbivores.
digest cellulose since most digestive systems cannot secrete cellulose digesting enzyme.
The bacteria and the herbivores are in a symbiotic relationship.
Assimilation
a) Glucose
important structural compound in plants.
b) Fatty acids and glycerol
c) Amino acids
Vitamins
are also obtained in fresh fruits and vegetables.
quantities.
influence the intake of certain substances. In particular, vitamin C influences uptake of
iron while vitamin D influences absorption of calcium ions in the gut.
deficiency diseases. These deficiency diseases can be corrected by inclusion of the
deficient vitamins in the diet or taking the vitamin supplements.
a) Fat soluble vitamins– They dissolve in fats and are often stored in the liver.
Include Vitamins A, D, E, K.
b) Water soluble vitamins– Dissolve in water. Include vitamins B1, B2, B5, B12 and
C.
Vitamin A (retinol)
main food source
uses in the body
deficiency disease symptoms
Vitamin B1 (thiamine)
main food source
uses in the body
deficiency disease symptoms
Vitamine B2 (riboflavine and nicotinic acid)
main food source
uses in the body
deficiency disease symptoms
Vitamin B5 (pentathonic acid)
main food source
uses in the body
deficiency disease symptoms
Vitamin B12 (cobalamine)
main food source
uses in the body
deficiency disease symptoms
Vitamin C (absorbic acid)
main food source
uses in the body
deficiency disease symptoms
Vitamin D (calciferol)
main food source
uses in the body
deficiency disease symptoms
Vitamin E (tosopherol)
main food source
uses in the body
deficiency disease symptoms
Vitamin K (quinone)
main food source
uses in the body
deficiency disease symptoms
Mineral salts
body functioning. Depending on body requirements, mineral salts are of two classes:
a) Macro-nutrients: Nutrients required in large quantities. These include nitrogen,
sulphur, phosphorous, calcium, sodium, iron and magnesium.
b) Micro-nutrients: Nutrients required in small quantities. Include copper,
manganese, boron, iodine and cobalt.
Element: Nitrogen
source
function in the body
deficiency symptoms
–
Element: Phosphorous
source
function in the body
deficiency symptoms
Element: Calcium
source
function in the body
deficiency symptoms
Element: Iodine
source
function in the body
deficiency symptoms
Element: Potassium
source
function in the body
deficiency symptoms
Element: Iron
source
function in the body
deficiency symptoms
Element: Sodium
source
function in the body
Element: Chlorine
source
function in the body
Element: Sulphur
source
function in the body
Element: Magnesium
source
function in the body
deficiency symptoms
Roughage
walls.
vegetables.
Importance of roughage
a) It rubs against the walls of the alimentary canal stimulating secretion of digestive
enzymes and mucus to lubricate the epithelial lining.
b) Roughage enhance peristalsis since as they rub against the walls of the alimentary canal,
they stimulate contraction and relaxation of the muscles.
c) Roughage is an absorbent; it extracts water from the alimentary canal making the fecal
matter bulky and moist hence can be easily propelled by peristaltic movements. This
prevents constipation.
Factors affecting energy requirements in humans
Discuss how the following factors affect energy requirements in humans:
Biology Notes FAQ Form
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