1. Living organisms are made up of one or more cells.
2.
Both animal and plant cells have a cell membrane, a
nucleus and a cytoplasm.
3. In addition, plant cells also have a cell wall, a vacuole
and chloroplasts.
chloroplasts
cell membrane
nucleus
vacuole
cell wall
cytoplasm
Animal cell
Cell structure
nucleus
cytoplasm
cell membrane
cell wall
vacuole
chloroplast
Plant cell
Function
Controls all of the cell’s activities and passes
on genetic information from one generation
to the next
The site of biological processes and
biochemical reactions e.g. respiration.
Controls movement of materials into and out
of the cell.
Provides support to the plant cell, and helps
the plant maintain rigidity.
Site of water and solute storage, and
maintains water balance through osmosis.
Absorbs light energy required in
photosynthesis.
Living cells summary booklet
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4. Cells are used commercially and in industries. Examples
of such uses are:
i.
Bread making – when yeast respires
anaerobically, carbon dioxide gas is produced.
Carbon dioxide bubbles get trapped in the
dough causing the bread to rise.
ii.
Alcohol production – during alcoholic
fermentation yeast produce alcohol as a waste
product.
iii.
Antibiotic production – fungi are used to kill
bacteria. These are known as antibiotics e.g.
penicillin. Some bacteria do show resistance to
some antibiotics though.
iv.
Yoghurt production – Some bacteria are
naturally present in milk and respire
anaerobically as they grow, producing lactic
acid. Lactic acid causes milk to curdle, thus
producing yoghurt.
v.
Alternative fuel production – Alcohol produced
through fermentation of sugar cane can be
mixed with petrol and used as fuel. Methane
produced by anaerobically respiring bacteria can
be used to produce biogas.
Living cells summary booklet
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1. Diffusion is the movement of the molecules of a
substance from a region of high concentration to a region
of low concentration, down a concentration gradient,
until both concentrations become equal.
This process can be seen below with the black molecules
diffusing through the clear molecules.
Equal concentration of
black molecules
throughout
High concentration
of black molecules
2. A number of substances enter and leave a cell by
diffusion e.g. oxygen, carbon dioxide, glucose, amino
acids, waste products.
amino acids
carbon dioxide
oxygen
waste products
glucose
3. Diffusion is extremely important in cells to:
i.
remove and reduce build up of waste products
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ii.
supply raw materials for respiration and
photosynthesis
4. Osmosis is a special case of water diffusion. Osmosis is
the movement of water from an area of high water
concentration to an area of low water concentration,
down a water concentration gradient, and through a
selectively permeable membrane.
5. Cell membranes are known as selectively permeable
membranes, because they contain tiny pores that only
allow small molecules e.g. glucose, water, oxygen
through, and do not allow larger molecules e.g. starch,
proteins through.
6. Osmosis is important to living cells, allowing water to
pass between cells and either nearby cells or the
surrounding environment. For example, water
movement in plants is as follows:
i.
soil solution (high concentration) → root hairs
(low concentration)
ii.
xylem vessels (high concentration) → stem cells
(low concentration)
iii.
xylem vessels (high concentration) → green leaf
cells (low concentration)
7.
If animal or plant cells are placed in an hypotonic
solution (a solution with a higher water concentration)
e.g. pure water, the cells will gain water by osmosis.
8.
If animal or plant cells are placed in an hypertonic
solution (a solution with a lower water concentration)
e.g. 1.0M sucrose solution, the cells will lose water by
osmosis.
9.
If animal or plant cells are placed in an isotonic solution
(a solution with the same water concentration), there will
Living cells summary booklet
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be no loss or gain of water – no osmosis (water
movement) will occur.
10.
Animal and plant cells react differently to hypoand hypertonic solutions due to the differences in these
cells. Remember plant cells contain a cell wall and
vacuole that animal cells do not.
Cell type
animal
animal
animal
plant
plant
plant
Solution type
hypotonic
isotonic
hypertonic
hypotonic
isotonic
hypertonic
Effect on the cell
cell bursts
cell remains unchanged
cell shrinks
cell becomes turgid
cell remains unchanged
cell becomes
plasmolysed
11. Plant
cells do not burst when they take up water due to
presence of a slightly stretchy cell wall. Plant cells
become turgid because the vacuole becomes filled with
water and expands pushing the cytoplasm against the
cell wall.
12. When
plant cells lose water they become plasmolysed,
which means the cell contents lose water and pull away
from the cell wall.
13. When
plant cells lose water, shrink in size and become
soft, they are described as being flaccid.
Living cells summary booklet
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1.
A catalyst is a substance that:
i.
lowers the energy input needed for a chemical
reaction to go ahead.
ii.
speeds up the rate of a chemical reaction.
iii. take part in the chemical reaction but remain
unchanged.
2. Enzymes are biological catalysts, which are made by
all living cells.
3. Enzymes are made of protein and are essential for the
functioning of all living cells.
4. The substrate is the substance on which the enzyme
acts e.g. starch is the substrate for amylase.
5. Each enzyme only acts on one substrate, thus enzymes
are therefore termed “specific” e.g. the enzyme amylase is
specific to the substrate starch.
6. The shape of the enzyme is complementary to the
substrate, thus the substrate is able to fit exactly into the
active site of the enzyme.
active sites
products
+
+
enzyme
substrate
Living cells summary booklet
Enzyme-substrate
complex
enzyme
page 6
7. Degradation is the enzyme-controlled breakdown of a
large complex substance into smaller molecules. An
example of a degradation reaction:
starch
amylase
(substrate)
maltose
(product)
8. Synthesis is the enzyme-controlled build-up of a large
complex molecule from smaller molecules. An example of
a synthesis reaction is:
phosphorylase
glucose-1-phosphate
(substrate)
9.
starch
(product)
Two factors that affect the activity of an enzyme are:
i.
temperature
ii.
pH
10.
The “optimum” temperature or pH for
an enzyme is the temperature or pH at which it works best,
thus has the greatest activity.
11.
as follows:
i.
ii.
iii.
The effect of temperature on enzymes is
At very low temperatures (0-10°C) enzyme
activity is very low, and therefore the rate of
the reaction is very slow.
As temperature increases to about 40°C the
enzyme activity and rate of reaction also
increase reaching a maximum at the optimum
temperature of 40°C.
At temperatures greater than 40°C the
enzyme activity and rate of reaction decrease
rapidly, reaching 0 between 50 and 60°C.
Over 50°C enzymes no longer work
because their structure becomes altered and the shape
12.
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active site is no longer complementary to the shape of the
substrate. Enzymes in this state are said to be denatured.
13.
Most enzymes work within the range of
pH5-pH9, with an optimum pH of 7 e.g. amylase.
14.
i.
ii.
Living cells summary booklet
Some exceptions include:
pepsin which works in the stomach,
working under acidic conditions, with
an optimum pH of 2.5
alkaline phosphatase is involved in bone
formation and has an optimum pH of 10
page 8
The chemical energy stored in glucose is released by a
series of enzyme-controlled reactions called respiration.
i.
ii. Some energy is released as heat from cells during
respiration.
iii. Most of the energy released is used for cellular
activities such as:
i.
muscle contraction
ii.
cell division
iii. synthesis of proteins
iv. transmission of nerve impulses
iv. The energy released from respiration (breakdown) of
glucose is used to synthesise adenosine Triphosphate (ATP)
from adenosine diphosphate (ADP) and phosphate (Pi).
adenosine
Pi
Pi + Pi
+
energy
(from respiration of
glucose)
enzyme
adenosine
Pi
Pi
Pi
v.
This ATP contains a high level of
chemical energy, and is thus an immediate and rapid
source of energy for a variety of activities in living cells e.g.
muscle contraction.
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vi.
Energy is released when ATP is
broken back down into ADP and Pi.
adenosine
Pi
Pi
bond which must be
broken to release energy
enzyme
adenosine
Pi
Pi
Pi + Pi
+
energy
(for cellular
activities)
Glycolysis is the process
where glucose is broken down into pyruvic acid, thus
yielding 2 molecules of ATP per molecule of glucose.
7.
8.
This pyruvic acid is then
broken down further. The end products of breaking down
pyruvic acid depends on whether oxygen is present or
absent.
aerobic
respiration
need for
oxygen
glycolysis
total energy
yield
end products
yes
anaerobic
anaerobic
respiration in respiration in
animals
plants
no
no
yes – 2ATP
38ATP
yes – 2ATP
2ATP
yes – 2ATP
2ATP
carbon
dioxide and
water
lactic acid
ethanol and
carbon
dioxide
Under anaerobic conditions in
animal cells, pyruvic acid is broken down into lactic acid in
9.
Living cells summary booklet
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a reversible process. This means that when oxygen
becomes available, repaying the oxygen debt, the lactic acid
is converted back into pyruvic acid.
10.
Lactic acid build-up in muscle
cells causes muscle fatigue.
Under anaerobic conditions
plants and yeast convert pyruvic acid to ethanol and carbon
dioxide in an irreversible process since the carbon dioxide
is lost.
11.
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1.
Photosynthesis is a series of enzymecontrolled reactions which allow green plants to make their
own food.
Plant cells have structures called
chloroplasts, which contain chlorophyll.
2.
It is this chlorophyll that captures light
energy from the sun and converts it into chemical energy
in the form of ATP.
3.
This ATP is used in the production of
4.
glucose.
5.
Photosynthesis can be summarized in the
following equation:
carbon water sunlight
glucose + oxygen
+
dioxide
chlorophyll
The carbon dioxide required for
photosynthesis diffuses into the leaf from the air through
the stoma (small pores on the surface of the leaf). Oxygen
produced during photosynthesis diffuses out of the leaf
through the stoma.
6.
7.
ii.
Photosynthesis has two stages:
photolysis – process where energy from
sunlight is used to split water molecules
into hydrogen and oxygen.
Living cells summary booklet
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iii.
8.
i.
ii.
iii.
carbon fixation – process in which carbon
dioxide from the air is combined with
hydrogen to make glucose.
During photolysis:
oxygen is released into the air as a by-product
ATP is made from ADP + Pi – this ATP is
passed onto and used during the carbon
fixation stage.
Hydrogen is released, picked up by a
hydrogen carrier molecule and passed onto
the carbon fixation stage.
9.
Carbon fixation involves a number of
enzyme-controlled reactions which use the ATP produced
during photolysis.
10.
The glucose produced during
photosynthesis can be turned into:
i.
starch – a storage carbohydrate composed of
200-800 glucose molecules forming a chain
e.g. plant food store
glucose unit
starch
molecule
ii.
cellulose – a structural carbohydrate
composed of 1000-1500 glucose molecules
forming a linear shape e.g. building material
present in plant cell walls.
glucose molecule
Living cells summary booklet
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cellulose
A limiting factor in photosynthesis is
anything which, when in short supply, reduces or limits
the rate of photosynthesis taking place e.g.
i.
light intensity
ii.
temperature
iii. carbon dioxide concentration
11.
12.
Horticulture is the cultivation of plants
especially in gardens and green houses.
13.
In horticulture, limiting factors are
removed by use of:
ii.
supplementary lighting
iii. carbon dioxide enrichment
iv. heating
in order to increase crop yields.
Living cells summary booklet
page 14