Download 1. General: state that cells are the basic units of living things

1. General: state that cells are the basic units of living
things.
 Sections of living tissue, when examined under a microscope
are seen to be made up of similar units.
 These units consist of cytoplasm, a nucleus and a membrane.
 These units are called cells.
 Living things can be distinguished from non-living things
because of their cellular structure.
2. General: Explain the purpose of staining animal and plant
cells.
 Some structures will be visible in unstained cells.
 Stains are taken up by some cell structures.
 More structures will be clearly seen in stained cells.
3. General: Describe the structural similarities of and
differences between animal and plant cells.
 Both animal and plant cells contain a nucleus, cytoplasm and a
cell membrane.
 Plant cells possess, in addition, a cell wall, chloroplasts and a
cell vacuole.
 Cells can be identified as plant or animal according to their
basic structure.
chloroplasts
cell membrane
nucleus
nucleus
vacuole
cell wall
cytoplasm
Animal cell
Investigating Cells Summary Booklet
Plant cell
page 1
4a. General: State that a substance can diffuse from a
high concentration to a low one.
 Diffusion occurs in gases and liquids.
 Gases and liquids are made up of
molecules.
low concentration of
 These molecules are moving all the
glucose inside the
cell
time, in a random way.
 The movement of molecules is faster
in a gas than in a liquid.
glucose
 Diffusion occurs when there is an
glucose
unequal distribution of molecules.
high concentration of
 Diffusion is the movement of
glucose outside the cell
molecules from an area of high
concentration to an area of low
concentration.
 Diffusion occurs until the molecules are evenly distributed.
4b. Credit: Explain the importance of diffusion to organisms.
 Gas exchange in organisms occurs in response to a concentration
gradient.
 Gas exchange takes place through the cell membrane in simple
organisms.
 There are organs for gas exchange in larger organisms.
5a. General: Give examples of substances which enter and
leave the cell by diffusion e.g. dissolved food, oxygen,
carbon dioxide and water.
 Glucose, oxygen and carbon dioxide pass through the cell
membrane by a process of diffusion.
 These substances must be dissolved in water.
5b. General: State that the cell membrane controls the
passage of substances into and out of the cell.
 The cell membrane contains tiny pores.
Investigating Cells Summary Booklet
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

Substances must be in a soluble form before they can
diffuse through the membrane.
Insoluble substances cannot diffuse through the membrane.
6a. General: Identify osmosis as a “special case” of the
diffusion of water.
 Osmosis is the movement of water molecules from an area
of high water concentration to an area of low water
concentration across a selectively permeable membrane.
 Osmosis occurs when two solutions of different
concentrations are separated by a membrane.
6b. Credit: Explain osmosis in terms of a selectively permeable
membrane and of a concentration gradient.
 A membrane, which allows molecules of all sizes to pass through, is
permeable.
 Membranes in living cells are selectively permeable. They do not
allow large molecules such as starch or proteins through.
 There are two selectively permeable membranes in plant cells – the
cell membrane and the vacuole membrane.
 A concentration gradient exists when there is an unequal distribution
of molecules. During osmosis, water molecules move down this
concentrations gradient, from the area of high water concentration to
the area of low water concentration, across a selectively permeable
membrane.
7. Credit: Explain observed osmotic effects in plants and in animal
cells in terms of the concentration of water in the solutions involved.
 Water diffuses from an area of high water
concentration to an area of low water
concentration.
plasmolysed cell
 When plant cells are placed in water (or a
weaker solution) they become turgid.
 When plant cells are placed in a more
concentrated solution they become flaccid.
 Plasmolysis occurs when a cell becomes flaccid.
turgid cell
Investigating Cells Summary Booklet
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8a. General: State that cell division is a means of
increasing the number of cells in an organism.
 Cell division (mitosis) occurs in special parts of a plant.
 Cell division (mitosis) and growth are separate processes.
 New cells arise from pre-existing cells.
8b. General: State that the nucleus of the cell controls cell
activities including division.
 Chromosomes carry information (genes).
 It is this information which controls the nature of the
organism.
 All the cells of the body contain the same number of
chromosomes.
9a. General: State that each of the two cells produced by
cell division has a complete set of chromosomes and the
same information.
 Each of the two daughter cells contain a nucleus with the
same number of chromosomes present in the original
nucleus.
 Each of the two daughter cells receive exactly the same
information, which is also the same as the information in the
original cell.
9b. Credit: Describe the stages of mitosis.
 The stages of mitosis are as follows:
i.
Chromosomes become visible in the nucleus.
ii.
Chromosomes then shorten. Each chromosome is made up
of 2 identical chromatids that are joined together at a point
called the centromere.
iii. Nuclear membrane disappears and the chromosomes line up
along the centre (equator) of the cell.
iv.
Spindle fibres attach to each of the centromere, and the two
chromatids that make up each chromosome are pulled to
opposite ends (poles) of the cell.
v.
A nuclear membrane forms around each group of
chromatids, thus completing nuclear division.
Investigating Cells Summary Booklet
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vi.
The cytoplasm then divides forming two daughter cells, each
with the same number of chromosomes and same
information as the parent cell.
9c. Credit: Explain why it is important that the chromosome
complement of daughter cells in multicellular organisms is
maintained.
 Chromosomes carry genetic information (genes).
 All processes in the cell are controlled by this information.
 It is therefore vital that this genetic information does not become lost
or altered through faults in cell division.
10. General: Identify the correct sequence of stages of
mitosis.
 The sequence of stages in mitosis is:
Stage 1 –
chromosomes not
yet visible in the
nucleus
Stage 6 – cytoplasm
splits to form 2 new
cells each identical
to the original cell
Stage 2 –
Stage 3 –
chromosomes visible chromosomes line up at
as 2 joined
the equator and spindle
chromatids
fibres attach at the
centromere
Stage 5 – chromatids
now called
chromosomes and
nuclear membrane
forms around these
Investigating Cells Summary Booklet
Stage 4 – spindle
fibres pull
chromatids apart
and to opposite
poles
page 5
11a. General: Explain why enzymes are required for the
functioning of living cells.
 Enzymes speed up the chemical reactions in living cells.
 For example, catalase, which is found in a variety of plant
and animal tissues, breaks down hydrogen peroxide with the
release of oxygen gas.
11b. General: Explain the meaning of the term “catalyst”.
 A catalyst speeds up a chemical reaction.
 A catalyst remains unchanged during the reaction.
 A catalyse repeats the reaction over and over again without
being changed.
 Enzymes are catalysts.
11c. Credit: Explain the term “specific” as applied to enzymes and
their substrates.
 The substance on which an enzyme acts is called its substrate.
 Each enzyme has a characteristic shape.
 A substrate molecule fits into the shape of the enzyme molecule at an
active site.
 The reaction takes place while the enzyme and substrate molecules are
fitted together.
 After the reaction has occurred the enzyme is released unchanged.
 Each enzyme can only react with one type of substrate molecule e.g.
amylase only reacts with starch.
products
active sites
+
+
enzyme
substrate
Enzyme-substrate
complex
Investigating Cells Summary Booklet
enzyme
page 6
12a. General: Give an example of an enzyme involved in the
chemical breakdown of a substance.
 The enzyme amylase breaks down starch into maltose.
 The word equation for this breakdown reaction is:
Starch
amylase
maltose
13a. General: Give an example of an enzyme involved in
synthesis.
 The enzyme phosphorylase is involved in the reaction by
which starch is made from glucose.
 In this reaction the glucose is in a special reactive form
called glucose-1-phosphate.
 The word equation for this synthesis reaction is:
Phosphorylase
Glucose-1-phosphate
starch
large
small
14a. General: State that enzymes are proteins.
 Enzymes are made from proteins.
14b. General: Describe the effect of temperature on
enzyme activity.
 The rate of enzyme activity increases with temperature up
to a maximum rate.
 Further increase in temperature results in a rapid decrease
in enzyme activity to zero.
 At high temperatures, proteins, and therefore enzymes are
denatured.
14c. General: Describe the effect of a range of pH on the
activity of pepsin and catalase.
 Pepsin breaks down protein.
 Pepsin has a narrow working pH range of pH2 – pH4.
Investigating Cells Summary Booklet
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

Catalase has a narrow working pH range of pH6 – pH9.
An enzyme does not function outside its working pH range.
An enzyme has a pH at which it functions best.
14d. Credit: Explain the term “optimum” as applied to the range of
conditions in which enzymes operate.
 The optimum temperature for an enzyme is the temperature at which it
has the greatest activity.
 The optimum pH for an enzyme is the pH at which it has greatest
activity.
 The optimum pH for pepsin is 2-3.
 The optimum pH for catalase is pH7.
 The optimum temperature for enzymes in humans is 37°C.
Investigating Cells Summary Booklet
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15. General: State three reasons why living cells need
energy.
 Living cells need energy for:
i.
cell division.
ii.
growth
iii. mechanical work and movement
iv.
uptake of chemicals
v.
building up molecules (chemical work)
16. Credit: State that fats and oils contain more chemical energy per
gram than carbohydrates or protein.
 Igniting a food sample releases chemical energy as mainly heat
energy, with some light and sound energy.
 This heat energy can be absorbed by water and brings about a
temperature rise.
 The temperature rise depends on the mass of the food, the mass of the
water and the nature of the food sample.
 Only the heat energy is absorbed by the water.
 Some of the heat energy heats the surrounding air and is not absorbed
by the water.
 Fats and oils contain twice as much energy per gram as carbohydrate
and protein, such that the calorific value per 1g burned is:
i.
fats and oils = 37kJ
ii.
carbohydrates = 17kJ
iii. proteins = 22kJ
17a. General: State that cells need oxygen to release
energy from food during aerobic respiration.
 In order for aerobic respiration to occur oxygen must be
readily available to cells, thus in order for energy to be
released from cells, through aerobic respiration, oxygen is
essential.
Investigating Cells Summary Booklet
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17b. General: Describe aerobic respiration in terms of a
word equation.
glucose + oxygen
raw materials






Carbon +
water + energy
dioxide
useful
waste products
product
Aerobic respiration occurs in a series of linked reactions
controlled by enzymes.
Whole organisms can be used in investigations of aerobic
respiration in cells.
The volume of oxygen taken in by an organism is equal to the
volume of oxygen given out.
A simple respirometer can be used to investigate oxygen
uptake by an organism.
A respirometer contains a chemical to absorb carbon dioxide
given out by the organism.
A respirometer must be kept at a constant temperature.
18. State that carbon dioxide is given off by cells during
tissue respiration and is derived from food.
 Carbon dioxide:
i.
turns lime water milky.
ii.
puts out a burning splint
iii. turns bicarbonate indicator solution from red
to yellow
 Certain chemicals can remove carbon dioxide from air.
 Both plants and animals respire to produce carbon dioxide.
 The carbon dioxide produced during respiration comes from
glucose.
Investigating Cells Summary Booklet
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19a. General: State that heat energy may be released
from cells during respiration.
 Energy released by respiration as heat may raise the
organism’s temperature above that of the surroundings.
Heat will therefore be lost to the surroundings.
 A differential air thermometer can be used to detect heat
being given off by organisms.
 Both plants and animals release some energy as heat.
 Energy released as heat is useful energy in some organisms,
but waste energy in others.
19b. Explain the importance of energy released from food during
respiration to the metabolism of cells.
 “Metabolism” describes all the chemical reactions taking place inside
a cell or a whole organism.
 Organisms convert chemical energy to other useful and waste forms.
 Wasted energy must be got rid of quickly.
 Heat energy may raise the temperature of the cell and increase the
reaction rates of enzyme-controlled reactions.
 Some reactions release energy as the reaction takes place.
 Some reactions require constant energy input to take place.
 Some reactions require a small initial energy input to take place.
 Energy release in cells must be controlled.
 A special chemical is continually formed and broken down and acts as
an energy store.
Investigating Cells Summary Booklet
page 11