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Learning Outcomes
What you need to
know
Unit 1
Tick off each piece of information once you have learned it.
A) CELL STRUCTURE AND FUNCTION

Animal cells have:- cell membrane, cytoplasm and nucleus.
Plant cells have:- cell membrane, cytoplasm, nucleus, vacuole, cell
wall and chloroplasts.
Functions of cell structures
Nucleus: Contains all the genetic information of the cell and controls
all activities within the cell e.g. cell division
Cell membrane: Thin barrier surrounding the cell to control the
entry and exit of certain substances.
Cytoplasm: Fluid, jelly like material in which all chemical reactions
are carried out.
Cell wall: A thick outer layer made of tough cellulose to provide
support and structure.
Vacuole: Fluid filled sac containing water and minerals as cell sap.
It regulates water content by osmosis
Chloroplasts: Contain chlorophyll which makes the plant green.
Trap light energy from sun needed for photosynthesis.
Commercial and industrial uses of cells
Bread making involves yeast undergoing anaerobic
respiration. The yeast produces carbon dioxide gas which
causes the dough to rise.
Alcohol production involves fermentation in yeast and results in the
production of alcohol (beer and wine)
Antibiotic production involves the use of fungi to produce a wide
range of antibiotics.
Antibiotics are substances produced by fungi which destroy
bacteria.
Resistant bacteria are unaffected by antibiotics and are on the
increase due to overuse of antibiotics.
Bacteria which are affected by antibiotics are said to be sensitive
to that antibiotic.
Yoghurt production. Bacteria convert the sugar in milk (lactose)
into lactic acid, causing curdling.
Alternative fuel production.
Biogas is produced when bacteria respire anaerobically to produce
methane from waste products.
Gasohol is produced when alcohol (produced by the fermentation of
sugar cane) is mixed with petrol.
B) DIFFUSION AND OSMOSIS IN PLANT AND ANIMAL
CELLS
Diffusion is the movement of substances from a high
concentration to a low concentration down a concentration
gradient.
Examples of substances which enter and leave a cell by
diffusion are:- glucose, amino acids (dissolved food),
oxygen, carbon dioxide and waste products (e.g. urea).
Diffusion is important to cells since it is the way in which
raw materials are gained for respiration and
photosynthesis. It is also the way in which waste products
are removed.
Osmosis is the movement of water from a high water
concentration to a low water concentration through a
selectively permeable membrane.
A hypotonic solution has a higher water concentration than
the water concentration within the cells.
A hypertonic solution has a lower water concentration than
the water concentration within the cells.
An isotonic solution has a water concentration which is equal
to the water concentration within the cells.

The effect of osmosis on plant cells is different to its effect
on animal cells due to their different structures.

Plant cells that have been in a hypotonic solution gain water
by osmosis and are said to be turgid.

Plant cells that have been in a hypertonic solution lose
water by osmosis and are said to be plasmolysed or
flaccid.

There will be no net movement of water by osmosis if a
plant cell has been placed in an isotonic solution.
TURGID CELL:
Water enters by osmosis,
vacuole swells and pushes
against the cell wall.
PLASMOLYSED/FLACCID CELL:
Water lost by osmosis, vacuole
shrinks and cell loses shape.
Animal cells, e.g. red blood cell
 A red blood cell placed in a hypotonic solution will take in
water by osmosis, swell up and may burst.

A blood cell placed in an isotonic solution will show no
change.

A red blood cell placed in a hypertonic solution will lose
water by osmosis and will shrink.
C) ENZYME ACTION

Catalysts
-Lower the energy input required for chemical reactions.
-Speed up chemical reactions.
-Take part in reactions but remain unchanged at the end.
Enzymes
-Are biological catalysts made by all living cells.
-Are made of protein.
-Are required for the functioning of all living cells.
-Are specific, they only work on one substrate. Each enzyme has its
own unique protein structure and overall shape which is designed to
match or complement the substrate on which it works.
Substrate
Enzyme
Starch
Hydrogen peroxide
Glucose-1-phosphate
Amylase
Maltose
Catalase
Oxygen + Water
Potato Phosphorylase Starch
Product
SAM
HPCOW
GPPPS
- Enzymes have a specific active site.
- Enzymes are involved in either degradation or synthesis reactions.
Degradation means the chemical breakdown of a substance.
- The enzymes you need to know that are involved in degradation
reactions are Amylase and Catalase.
- Synthesis means the building of a complex molecule from simpler
molecules.
- The enzyme you need to know that is involved in a synthesis reaction
is phosphorylase
- Enzyme activity is affected by pH and temperature.
- The pH at which an enzyme works best is its optimum pH.
- Generally, enzymes work better as the temperature increases.
BUT……This works only up to a point.
- The temperature at which the enzyme works at its fastest rate is
called the optimum temperature.
- Most human enzymes have an optimum temperature of (37ºC).
- At very high temperatures, enzymes will denature, this means that
shape of the enzyme’s active site is changed and the enzyme will no
longer work.
D) Aerobic and anaerobic respiration
- Glucose is the source of energy in a cell.
- The chemical energy stored in glucose is released by a series of
enzyme controlled reactions called respiration.
- Some energy is released as heat from cells during respiration but
most is used for cellular activities such as muscle contraction, cell
division, synthesis of proteins and transmission of nerve impulses.
- Energy released from the breakdown of glucose is used to synthesise
ATP from ADP and Pi. The ATP can then be used by the cell as an
energy source.
- Aerobic respiration yields 38 molecules of ATP per glucose molecule.
-Anaerobic respiration yields 2 molecules of ATP per glucose molecule.
Aerobic pathway
Glycolysis : Glucose is broken down into pyruvic acid.
The pyruvic acid is then broken down to carbon dioxide and water.
Oxygen is required to do this.

Anaerobic pathway
Glycolysis: Glucose is broken down into pyruvic acid.
The pyruvic acid is then converted to lactic acid in mammals. (This
conversion is reversible and will convert back to pyruvic acid if the
oxygen debt is repaid.)
Lactic acid causes muscle fatigue.
The pyruvic acid is converted to ethanol and carbon dioxide in plants
and yeast. This conversion is irreversible.
E) Photosynthesis

- Photosynthesis is a series of enzyme-controlled reactions which allow
green plants to make their own food.
- Sunlight is the source of energy for photosynthesis.
- The light energy from the sun is trapped by chlorophyll in the
chloroplasts and is converted into chemical energy in the form of ATP
which is then used in the production of glucose.
Summary equation of photosynthesis is:Water + carbon dioxide + light energy 
Raw materials
(absorbed by
the
chlorophyll)
glucose
Food
product
+
oxygen
By product
Diffusion is very important in the movement of carbon dioxide and
oxygen into and out of the leaf cells.
Photosynthesis is a set of 2 summary reactions: - photolysis followed by
carbon fixation.
Photolysis
Is the breakdown of water to provide hydrogen, ATP and oxygen.
The oxygen is released as a by-product and the hydrogen is
picked up by a hydrogen carrier molecule.
Carbon fixation
Is the combining of the hydrogen produced by photolysis with carbon
dioxide to form glucose using the ATP produced during photolysis.
Glucose formed during carbon fixation is converted to other
carbohydrates e.g. starch and cellulose.
Starch is a storage carbohydrate
Cellulose is a structural component of the cell wall.
Factors affecting the rate of photosynthesis
1) Limiting factors
A limiting factor in photosynthesis is anything which when in short
supply, reduces or limits the rate of photosynthesis taking place.
Limiting factors can be light intensity, carbon dioxide concentration
and temperature.
(In any question on limiting factors, the factor on the X axis remains a
limiting factor for as long as the graph continues to rise; in this case
the point at which it levels off. At this point photosynthesis may still be
limited by other factors such as temperature or carbon
dioxide concentration.)
2) Production of early crops in horticulture
Supplementary lighting, carbon dioxide enrichment and heating will
help to produce early crops in horticulture.