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CELL PROCESSES
What is a cell?
It is the basic unit of life
Types of cells

There are two types

 Animal
 Plant

Structure of animal cell

Structure of plant cell

STRUCTURE PROPERTIES FUNCTIONS

Cell membrane 2 lipid layer with one Controls passage of
protein layer sandwiched in dissolved substances
between into and out of the cell
Nucleus Contains genetic material Regulates cellular
(chromosomes) activities i.e. chemical
reactions and activities
of the cell
Cytoplasm Contains water & dissolved Where biochemical
substances e.g. glucose, reaction take place
minerals, vitamins
Ribosome Small grains found Responsible for building
scattered in the cytoplasm, up of the cell’s proteins
some may be attached to (proteinsynthesis)
endoplasmic reticulum
mitochondrion Surrounded by 2 Site for aerobic
membranes, inner respiration
membrane has folds
Cell wall Made carbohydrate called Protects cell against
cellulose, its freely mechanical damage &
permeable gives plant a permanent
shape
vacuole Has concentrated Stores the cell sap (vital
solution made of salts, chemicals for the cell)
glucose and pigment Maintains pressure in
the cell
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SPECIALIZED CELLS
These are cells which have stopped growing, have a definite shape and perform one specific
function and have special kinds of chemical reactions that enable them to carry out its specific
function.

Examples of specialized cells.

Cell Function Relationship between structure & Function.

1. Red Blood Cells Responsible for transporting - Has a biconcave and disc shaped structure
(Erythrocytes) O2 that helps it move in the blood vessels
- Has a spongy cytoplasm that helps it to
compress itself in blood vessels with small
lumen
- Absence of nucleus increases surface area
for absorption and transportation of O2
- Presence of haemoglobin that binds easily to
O2 and carry it as an unstable compound
called oxyhaemoglobin
2. Muscle cell It moves bones in different - Long and thin & have numerous protein
directions (contract / relax to fibres in the cytoplasm. (fibre helps to shorten
help move structures) the cell when there is energy)
- Can of contract & relax in order to move
parts

3. Sperm cell Fuse with ovum to from a - Has streamlined head to enable it to move
zygote towards ovum with less friction
- Has a tail to help it swim towards the ovum.

4. Ovum Fuse with sperm to from a - It has a large food store to provide the zygote
zygote with nourishment before implantation

5. White Blood Cells Phagocytes – engulf & digest - Phagocytes are polymorphs; can change
(Leucocytes are two bacteria (pathogens) shape of cytoplasm and pass through blood
types; Phagocytes vessels like amoeba.
& Lymphocytes) Lymphocytes – produce - Have Granular cytoplasm with lobed nucleus.
chemicals called antibodies
that kill bacteria

6. Root hair cell - Absorb water from the soil - Large number of mitochondria to generate
- Absorb mineral ions energy needed for active transport of ions
(salts) from the soil - Has a projection that enables to penetrate
- anchor the plants firmly to tightly packed soil particles
the ground. - Have Large concentrated sap vacuole which
ensures water uptake through osmosis
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7. Xylem cells - Transport water & - Has dead hollow tube without cytoplasm to
dissolved minerals from the allow flow of water
roots to top part of a plant - Walls are lignified (coated with lignin) to
- Supports the plant against withstand water pressure
mechanical damage - cylindrical cells are attached end to end form
a xylem vessel.

8. Nerve Cell Transmits nerve impulses - Have very long fibres which connect distant
(neuron) (messages) around the parts of the body
body - Fibres are coated with sheath to prevent loss
& distortion of messages.
- Chemical reactions cause the impulses to
travel along the fibre

9. Palisade cell To make sugar (starch) - Has lots of chloroplasts to produce

through photosynthesis chlorophyll which traps sunlight energy for
the process
- Elongated so that they can pack tightly
- Located close to the upper epidermis to
receive more sunlight

10. Guard cells To regulate the opening & - Crescent shaped

closing of stomata allowing - Always paired to form a stomata
for gaseous exchange - Are able to change shape to close / open
between the leaf and the depending on whether its day or night.
atmosphere
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Cell
Cell Organization
Organization

Cells
Cells are
are organized
organized into
into tissues,
tissues, organs,
organs, systems
systems and
and ultimately
ultimately an
an
organism
organism (plant
(plant // animal)
animal)

A
A Cell;
Cell; is
is the
the basic
basic unit
unit of
of life
life
A
A Tissue;
Tissue; is is aa group
group of of similar
similar cells
cells carrying
carrying out
out the
the same
same function.
function. E.g.
E.g.
xylems cells make xylem
xylems cells make xylem tissue tissue
An
An Organ;
Organ; is is aa group
group of of different
different tissues
tissues which
which work
work together
together toto
perform
perform aa particular
particular function.
function. E.g. E.g. the
the heart
heart is
is organ
organ made
made ofof nerve
nerve
tissue,
tissue, muscle
muscle tissue,
tissue, epithelial
epithelial tissue
tissue etc.
etc.
A
A System;
System; is is aa group
group ofof organs
organs which
which work
work together
together to to perform
perform aa
particular
particular function.
function. E.g. E.g. the
the digestive
digestive system
system is
is made
made of;
of; stomach,
stomach,
mouth,
mouth, intestine,
intestine, liver
liver etc
etc
An
An Organism;
Organism; Is Is aa group
group of of different
different systems
systems which
which come
come together
together toto
form
form a living thing e.g. Human beings are made of; nervous, skeletal,
a living thing e.g. Human beings are made of; nervous, skeletal,
circulatory,
circulatory, digestive,
digestive, muscle
muscle systems
systems etc.etc.
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Movement of Substances in & out of cells

There are three processes that are involved in the movement of substances in & out cells
 Diffusion
 Osmosis
 Active transport

1. Diffusion;
It is the random movement of particles from their region of their higher concentration to their
region low concentration down a concentration gradient until they are evenly distributed.

N.b. Diffusion occurs in all states of matter.

a) Diffusion in gases
The spread of perfume particles (or air freshener) from the nozzle of the spray can to fill up the
room occurs through diffusion.

b) Diffusion in liquids
The spread of potassium permanganate from the bottom of a beaker to the top is by diffusion.

Diffusion is affected by;

I. Changes in temperature;
An increase in temperature increases the kinetic energy of particles; hence particles
will move faster leading to an increase in the rate of diffusion

II. Particle size

Small particles dissolve faster because they are less dense & have a large surface area
hence can diffuse rapidly from one end to the other.

III. Concentration gradient

This is the difference in the amount of particles between two adjacent areas. Particles
move faster when the difference in the amount of particles is large. The rate of
diffusion diminishes as the concentration gradient reduces.

2. Osmosis;
It is the random movement of water molecules from their region of higher concentration to their
region of lower concentration along the concentration gradient through a partially / selectively
permeable membrane.

Similarities between Osmosis & Diffusion

 Particles are moving down or along the concentration gradient
 Both processes are passive, no energy is expended (used)

Differences between Osmosis & Diffusion

OSMOSIS DIFFUSION
Occurs mainly in liquids (only water Occurs in all states of matter (any particle is
molecules are moved) moved)
Materials are moved across a barrier (a Does not require a barrier (partially
partially permeable membrane required) membrane)

3. Active Transport
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This is the movement of materials from their region of low concentration to their region of high
concentration against the concentration gradient using energy from respiration. Substances are
moved through the aid of protein carrier molecules and a barrier is not important.

Active transport is different from the other two modes of movement in that;
 Unlike osmosis & diffusion, it occurs against the concentration gradient
 It requires energy
 Only mineral ions are moved

Osmosis and cells;

A cell can be exposed to the following conditions;
 Immersed in pure (distilled) water / dilute solution
 Immersed in a concentrated solution

??? Explain what happens when a plant cell is immersed in pure water / dilute solution

Ans; There will be an influx of water from the container into the cell by osmosis leading to
an increase in the contents of the protoplasm. As a result turgor pressure builds inside the
cell membrane causing it to stretch until it touches the cell wall. When this happens the
cell is said to be Turgid.
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??? Explain what happens when a plant cell is immersed in a concentrated solution.

Ans; the water molecules will move out of the cell by osmosis. The outflux of water
molecules will lead to a decrease in the contents of the protoplasm hence a decrease in
turgor pressure. The cell membrane will become flaccid and pull away from the cell wall.
When this happens the cell is said to be plasmolysed.

??? Explain what happens when an animal cell is immersed in pure water / dilute solution

Ans; Water molecules will move into the cell by osmosis and due to build up of turgor pressure
the cell membrane will burst (since the animal cell has no cell wall to limit the stretching of the
membrane).

??? Explain what happens when a animal cell is immersed in a concentrated solution.

Ans; Due to outflux of water by osmosis, the cell will decrease in size and when this happens the
cell is said to be shrunken.
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ACTIVITY; The Effect of various sugar concentrations on potato tissue

Apparatus & materials

 5 different solns; 0%, 5%, 15%, 25% and 60%
 5 petri dishes
 Cork borer
 White tile
 Scalpel
 30cm ruler
 Large potato
 25ml measuring cylinder

Procedure
- Label the petri dishes A to E.
- Place equal volumes (10ml) of the sugar concentrations in the petri dishes as; 0% in petri dish A
5% in dish B, 15% in dish C etc.
- Prepare 5 equal sized e.g. (40mm) potato slices by boring the potato using a cork borer
- Place one potato slice in each petri dish.
- Leave the potato slices in the solutions for 30 – 60 minutes. The remove the slices & blot them with
a paper tissue.
- Measure the final lengths of the slices and record the results as follows

Sugar soln Initial length Final length Change in length

0%
5%
15%
25%
60%

Practice Questions on the activity above;

 Plot a graph of sugar concentration against change in length
 From the graph, work out the concentration of the potato tubes
 At what concentration would the concentration of the sap vacuole of the potato equal that
of the surrounding sugar soln?
 What process is responsible for the change in length of the potato tubes?
 What is the formula for calculating the change in length of the potato tubes?
 What else can be measured to find out the effect of concentration on the potato slices?