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CELL PROCESSES & MAINTENANCE

-identify different parts of plant and animal cells (mitochondria, ribosome, nucleus, cytoplasm, cell membrane common in
both plant and animal cells. Cell wall, chloroplast, vacuole in plant cell only)
- state the functions of each part of a cell.
CELL SPECIALISATION AND ORGANISATION
- describe the relationship between cell structure and function using an animal cell and a plant cell as
examples
- define tissue, organ, system, and organism.
MOVEMENT OF SUBSTANCES IN AND OUT OF CELLS
- define diffusion as movement of molecules from a region where they are at a higher concentration to a
region where they are at a lower concentration i.e. down a concentration gradient.
- demonstrate diffusion in gases and liquids.
- describe how concentration gradient, particle size and temperature affect diffusion rate.
- define osmosis (a special form of diffusion) as movement of water molecules from a region where
they are at a higher concentration to a region where they are at a lower concentration through a selectively permeable
membrane.
- describe the effect of concentration gradient in the uptake of water by plants.
- describe the effect of osmosis on plant tissues, in terms of turgid cells, flaccid cells and plasmolysis
- describe the effect of osmosis on animal tissues in terms of bursting and shrinking
- conduct experiments using solutions of varying concentration to demonstrate the process of osmosis.
- define active transport as an energy consuming process in which substances are transferred against their concentration
gradient.
- define passive transport as a non-energy consuming process in which substances are transferred down their concentration
gradient.
BIOLOGY is a science that studies LIFE or living things

CHARACTERISTICS OF LIVING THINGS

Living things
 RESPIRE
 ARE SENSITIVE TO STIMULUS
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 MOVE
 GROW
 REPRODUCE
 EXCRETE
 FEED
 All living things are made up of very small units called CELLS. Therefore, cells are referred to as the basic unit of life.

Chemical reactions which sustain LIFE occur inside cells. These chemical reactions are called METABOLIC REACTION or
METABOLISM. These cells can be studied in detail through the use of a tool called a MICROSCOPE since cells are not visible to
the naked human eye. This tool ENLARGES/MAGNIFIES them for them to be studied in detail.

Types of cells
There are two types
 Animal cells
 Plant cells

Structure of animal cell

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Structure of plant cell

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Common parts in plant and animal cells are cell membrane, cytoplasm, nucleus, ribosome and mitochondria.

Differences between plant and animal cell

PLANT CELL ANIMAL CELL

-have cell wall, chloroplast and vacuole -have no cell, no chloroplast and no
vacuole

FUNCTIONS OF PARTS OF A CELL

STRUCTURE PROPERTIES FUNCTIONS

Cell membrane Two lipid layer with one protein layer Selects/controlls substances entering & leaving
sandwiched in between the cell. This is refereed to as being selectively
permiable
Nucleus Contains genetic material called chromosomes Regulates/controls all cellular activities taking
place in the cell
Cytoplasm Contains water & dissolved substances e.g. Where biochemical reaction take place
glucose, minerals, vitamins
Ribosome Small grains found scattered in the cytoplasm, Responsible for protein formation
some may be attached to endoplasmic reticulum
mitochondrion Surrounded by two membranes,inner membrane Site for aerobic respiration
has folds
Cell wall Made of carbohydrate called cellulose, its Protects cell against mechanical damage & gives
strong and freely permeable plant a permanent shape
vacuole Has concentrated solution made of dissolved Stores the cell sap
salts, sugars
chloroplast Produces chlorophyll - A site for photosynthesis
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SPECIALIZED CELLS
These are cells which have stopped growing, have a definite shape and perform one specific function.
Examples of specialized cells.

Cell Function Relationship between structure &

Function.
1. Red Blood Cells Responsible for - Has a biconcave structure that
(Erythrocytes) transporting allows it to easily move in the blood
oxygen from vessels
the lungs to the - Has a spongy cytoplasm that helps
rest of the body it to compress itself in blood vessels
cells. with small lumen
- Absence of nucleus increases
space for transportation of more
oxygen
- Presence of protein haemoglobin
that easily binds to oxygen when in
areas where the concentration of
oxygen is high and carry it as an
unstable compound called
oxyhaemoglobin. Oxyhaemoglobin
easily dissociates to release oxygen
when the red blood cell is in areas
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where oxygen is low in

concentration.
2. Muscle cell -it is long and has numerous protein
It moves bones fibres in the cytoplasm which can
in different contract & relax in order to move
directions parts of the body

3. Sperm cell - Has streamlined head to enable it

Fuse with ovum to move towards ovum with less
to from a zygote friction
- Has a tail to propel it as it swims
towards the ovum.

4. Ovum Fuse with - It has a large food store to provide

sperm to from a the zygote with nourishment before
zygote implantation
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5. White Blood Cells

(LEUCOCYTES: are of two
types; Phagocytes &
Lymphocytes)
Phagocte
i. Phagocytes - Phagocytes has a lobed nucleus
– engulfs & which allows it to easily change
digest shape to engulf a pathogen.
pathogens

Lymphocyte
ii.Lymphocytes ii. it has a large nucleus that is able
– produce to produce many different types of
chemicals antibodies
called
antibodies that
kill phathogens
Antibodies act
on pathogens in
several ways :
- weakening
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and clumping
pathogens so
that they can be
easily engulfed
by phagocytes
- Dissolve
their cell
membrane
-Neutralize
toxins from
pathogens

Ciliated hair cell -protect the -has goblet cells which produce
respiratory tract mucus that traps the dust particles
against the and phathogens
invasion of -has cilia which flips to sweep out
phathogens the mucus.
and dust Cilia on the linning of the fallopian
particles tubes moves the ovum from the
ovum during ovulation
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6. Root hair cell - Absorb water - Large number of mitochondria to

from the soil release energy needed for active
-Absorb transport of dissolved ions into the
dissolved root hair cell.
mineral - Has a finger-like projection that
salts/ions from increases surface area to absorb
the soil more water and mineral ions. It also
enables the plant to penetrate tightly
packed soil particles
- Have Large concentrated sap
vacuole which ensures water uptake
through osmosis

7.Phloem cells -translocate - made of living cells

organic food -has sieve plates with sieve tubes
molecules that allows food molecules to move
from one phloem cell to another
-no nucleus and vacuole so that
movement of food molecules is not
disturbed
-has companion cells that contains
all organells and carry out metabolic
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processes that support the living

phloem cells
8. Xylem cells - Transport - it is made of dead cylindrical cells
water & attached end to end without
dissolved partitions.There are no organells
minerals salts and cytoplasm to form a hollow tube
from the roots through which water freely flows.
to top part of a
plant
-Walls are lignified (coated with
lignin) which is a very strong
substance that enable the xylem to
withstand water pressure and not to
- Supports the move/collapse inward the xylem.
plant against Lignin is also water proof therefore
mechanical allows efficient transportation of
damage water without
loss

8. Nerve Cell (neuron) Transmits nerve - Have very long fibres which
impulses connect distant parts of the body
around the - Fibres are coated with fat sheath
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body called myelin to prevent loss of

electrical impulses & distortion of
electrical messages.

9.Palisade mesophyll cell -Where - Has lots of chloroplasts to trap

maximum maximum sunlight energy for
photosynthesis maximum process of
take place photosynthesis.
- Elongated so that they increase
surface area for maximum
photosynthesis
-are closely packed to have
maximum access to sunlight
- Located close to the upper
epidermis to receive more sunlight
for more photosynthesis
.

10. Guard cells To regulate the - Crescent shaped

opening & - Always paired to form a stomata
closing of - Are able to change shape to close
stomata or open the stomatal pore.
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-have chloroplasts that absorbs

sunlight and stimulate the uptake of
water into the guard cell by osmosis.
This influx of water result in the
guard cell walls being turgid and
opening up the stomata

Cell Organization

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

 A Cell; is the basic unit of life

 A Tissue; is a group of similar cells carrying out the same function. E.g. xylems cells
make xylem tissue
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 An Organ; is a group of tissues which work together to perform a particular function. E.g.
the heart is organ made of nerve tissue, muscle tissue, epithelial tissue etc.
 A System; is a group of organs which work together to perform a particular function. E.g.
the digestive system is made of; stomach, mouth, intestine, liver etc
 An Organism; Is a group of different systems which come together to form a living thing
e.g. Human beings are made of; nervous, skeletal, circulatory, digestive, muscle systems
etc, a plant is made of the shoot system and the root system.

MOVEMENT OF SUBSTANCES IN AND OUT OF CELLS

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

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

a) Diffusion in gases
example: 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
example: The spread of potassium permanganate from the bottom of a beaker to the top is
by diffusion.
Diffusion is faster in gases than in solids because particles in gases are further apart can
move very fast.

FACTORS AFFECTING THE RATE OF DIFFUSSION;

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 move faster because they are less dense hence can diffuse rapidly
from one end to the other.

III. Concentration gradient

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This is the difference in the amount of particles between two adjacent areas. If the
difference in the amount of particles is large, we say the concentration gradient is
high/large. If the difference in concentration of the particles is small, we say the
concentration gradient is low/small.
Particles move faster when the difference in the amount of particles is large, that is
when the concentration gradient is large. The rate of diffusion diminishes as the
concentration gradient reduces.

2. Osmosis;
It is the random movement of free water molecules from their region of higher concentration
to their region of lower concentration (down their concentration gradient) through a
selectively permeable membrane.

Similarities between Osmosis & Diffusion

 In both processes particles move down their concentration gradient
 Both processes are passive, no energy is needed to move the particles

Differences between Osmosis & Diffusion

OSMOSIS DIFFUSION
Only free water molecules Any particle moves.
move.
Water molecule move across Does not require a selectively
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a selectively permeable membrane. Particles freely

membrane which acts as a move
barrier.

3. Active Transport
This is the movement of materials from their region of low concentration to their region of
high concentration (against their concentration gradient) using energy from respiration.
Substances are moved with the aid of protein carrier molecules and a barrier.

Differences between Osmosis/Diffusion and Active transport

Active transport is different from the other two modes of movement in that;
OSMOSIS /& DIFFUSION ACTIVE TRANSPORT
-occurs down their -occurs against their
concentration gradient concentration gradient
-They are passive processes, -is an active process, energy
energy is not required to is required to move the
move particles particles
-Can take place in non living -only take place in living cells
matter
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EFFECTS OF OSMOSIS ON PLANT CELLS

A cell can be exposed to the following conditions; Immersed in

 pure water
 distilled water
 a dilute solution
 a high water potential solution (a high water concentrated solution compared to the
cell)
 a low solute concentrated solution
 a hypotonic solution

OR
Immersed in
 a concentrated solution
 low water potential solution (a low water concentrated solution compared to the cell)
 a high solute concentrated solution
 a hypertonic solution

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

Ans;
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-Pure water has high water potential than plant cell, -therefore water
molecules will move from the pure water into the cell
-through a selectively permeable membrane 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.

Explain what happens when a plant cell is immersed in a concentrated solution/ low water
potential solution?
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Ans;
-A plant cell has high water potential than a concentrated solution it has been placed in,
-therefore the water molecules will move out of the cell into the concentrated solution
-through a selectively permeable membrane by osmosis
- leading to a decrease in the contents of the protoplasm hence a decrease in turgor
pressure exerted on the cell wall. When this happens the cell is said to be flaccid.

If water loss from the plant cell into the concentrated solution continues, the cell
membrane will pull away from the cell wall. When this happens the cell is said to be
plasmolysed.
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EFFECT OF OSMOSIS ON ANIMAL CELLS

Explain what happens when an animal cell is immersed in pure water / distilled water/ dilute
solution/ high water potential solution?
Ans;
-Pure Water has high water potential that animal cell,
-so water molecules will move from pre water into the cell
-through a selectively membrane by osmosis
-The cell will increase in size due to build up of pressure and the cell membrane will
eventually burst, since the animal cell has no cell wall to limit the stretching of the cell
membrane.

Explain what happens when an animal cell is immersed in a concentrated solution/ low
water potential solution?

Ans;
-Animal cell has high water potential than the concentrated solution
- therefore there will be an outflux of water from the cell into the concentrated solution
-through a selectively permeable membrane by osmosis,
- the cell will decrease in size and shrink
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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

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0%
5%
15%
25%
60%

Questions on the activity above;

 What is the formula for calculating the change in length of the potato tubes?
 Calculate the change in length of each potato tube.
 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 solution?
 What process is responsible for the change in length of the potato tubes?
 What else can be measured to find out the effect of concentration on the potato slices?
-Suggest what could be done to improve the reliability/accuracy of the experiment.