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Section C: Plant Physiology
Chapter 10: Plants and food 1 photosynthesis light chlorophyll
chloroplasts water sugar (glucose) starch
2 a) Carbon dioxide gas is absorbed from the air.
Water from the root moves up to the leaf through the stem.
Sunlight provides energy.
Sugars are made in the leaf and provide the plant with food.
Oxygen is produced and released into the air.
b) Carbon dioxide + water + energy from the Sun sugar +
oxygen
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4 a) Starch
b) The mass of the potato crop depended on the amount of
sunlight in the growing season, being larger with more sunlight and
smaller with less. Most of the mass of a potato is made of starch,
and starch is made as a direct result of photosynthesis. The amount
of photosynthesis that can take place depends on the amount of
sunlight available to supply the energy, so the amount of sunlight
is directly linked to the size of the potato crop.
5 a) Any five from
Product made How it is used in the plant cells
starch storage compound
cellulose cell walls
protein cytoplasm, enzymes
DNA genetic material, contains instructions for making new
cells, etc.
chlorophyll captures light energy for photosynthesis
sucrose for transport around the body
amino acids to build up into proteins
b) Respiration to supply energy for the cells
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6 a)
b) The palisade layer is closely packed with lots of
chloroplasts and close to the surface of the leaf so that it can
capture as much light as possible for photosynthesis.
The spongy layer consists of loosely packed cells with lots of
air spaces, giving a large available surface area for gaseous
exchange between the cells and the air, while the chloroplasts
allow some photosynthesis to take place.
The upper epidermis protects the cells in the leaf from damage.
It is transparent so that light passes through to the palisade
cells beneath.
The chloroplast is the cell organelle that contains chlorophyll,
the green pigment that captures light energy for
photosynthesis.
A stoma (plural stomata) is a pore that allows gases to diffuse
into and out of the leaf.
A guard cell controls the opening and closing of the
stomata.
7 a) Bubbles of gas escape from the end of the stem.
b) i) More bubbles / It would bubble faster.
ii) Fewer bubbles/ It would bubble more slowly.
c) Because plants need light for photosynthesis. If they have
more light, they can photosynthesise faster, but with less light
they will photosynthesise more slowly.
d) The temperature might be changing because the light gets
hot.
8 a) Correctly plotted graph with labelled axes, etc.
b) Seedlings in 85% sunlight receive much more light energy than
those in 30% sunlight. This means they can carry out more
photosynthesis and use the sugars they make to build up more new
tree. Thus the seedlings grown in higher light levels grow taller
than those grown in lower light levels.
9 a) 2530C
b) It causes a steady increase in the rate of photosynthesis up
to around 30C, after which the rate of photosynthesis starts to
fall.
c) 50C
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d) Because in respiration the plant uses the food it makes in
photosynthesis, so when the difference between the two is greatest,
the largest amount of sugar will be available to turn into tomato,
resulting in the biggest crops.
e) 25C
10 Plant A is lacking in potassium and needs a potassium-rich
fertiliser.
Plant B is lacking in nitrogen and needs a nitrogen-rich
fertiliser.
Plant C is lacking in phosphate and needs a phosphate-rich
fertiliser.
Chapter 11: Transport in plants 1 a) There is a lower
concentration of water molecules inside the membrane bag than
outside it.
There is a lower concentration of sugar molecules outside the
membrane bag than inside it.
Water molecules move into the bag by diffusion along a
concentration gradient through the partially permeable
membrane.
Sugar molecules are too large to pass through the membrane by
diffusion, so the imbalance of molecules and the diffusion gradient
for the water molecules are maintained.
Water continues to move into the bag by osmosis, so the water
level in the tube rises.
b) Because the root hair cell is similar to the partially
permeable membrane bag. Water moves into the cell from the soil
along a concentration gradient, but sugars, etc., cannot leave the
cell.
c) Sugars such as glucose are osmotically active, so a build-up
of these sugars in cells would lead to the movement of water into
those cells by osmosis. This water movement might not be useful to
the plant.
Starch is not osmotically active, so carbohydrates can be stored
in plant cells in the form of starch without causing water to move
into the cells as well.
Plants can move water internally by converting glucose to starch
or vice versa.
d) Active transport it uses energy.
e) The constant evaporation of water from the leaves causes
water molecules to be pulled up through the plant transport system
as the water molecules stick together. Thus water is constantly
being removed from the roots, raising the concentration of the
cytoplasm in the root hair cells and thus causing water to move
into those cells by osmosis from the soil water around the
roots.
f) Because the roots have a large surface area, many root cells
are in close contact with soil and soil water, so a lot of water
can move by osmosis from the soil into the roots.
2 a) The cell contents contain a much higher concentration of
solutes than the distilled water. The solution is much more
concentrated, so has a much lower concentration of water. This
means that water moves into the cells making up the cylinders by
osmosis down a concentration gradient. The cells become very turgid
and expand, so the potato cylinder expands.
The weak sugar solution has a similar concentration to the cell
contents, so there is little or no net movement of water by osmosis
and the cylinders stay the same.
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The strong sugar solution is more concentrated than the cell
contents. Water moves out of the potato cells by osmosis. They
become flaccid or plasmolysed, so the cylinder shrinks.
b)
3 support stomata transpiration waxy
4
5 Water loss by evaporation in a plant is known as
transpiration.
Plants keep relatively cool in hot sun because transpiration
cools them down.
Transpiration also creates a risk that the plant will lose too
much water and wilt.
Transpiration is more rapid in hot, dry and windy
conditions.
6 a) In the leaves (and in the green parts of the stem, from
high-ability pupils)
b) Through the roots in the soil
c) Xylem
d) Phloem
e) Xylem
f) Phloem cells are living, xylem cells are dead.
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7 a) A process by which a plant loses water from the leaves by
evaporation through the stomata
b) The waxy cuticle.
c) Very little effect, as the waxy cuticle is on the top surface
and most stomata are on the bottom of the leaf.
d) Most stomata are on the lower surface of leaves. Vaseline on
the lower surface would cover the stomata, preventing the loss of
water by evaporation and so slowing the rate at which water is
taken up.
e) The air bubble would move rapidly towards the plant, because
the fan would increase the rate of water lost by evaporation from
the surface of the leaves and so the uptake of water would
increase.
f) Uptake of water, not water lost by transpiration. A small
amount of the water taken up will be used for photosynthesis,
etc.
Chapter 12: Chemical coordination in plants 1 stimuli light
gravity growing hormones
2 a) towards
b) away from
c) towards
3 a)
b) A: The tip makes a hormone in response to one-sided light and
this passes down to the growing region. The shoot grows more on the
dark side and so bends towards the light.
B: As A. The hormone is water soluble and passes through the
agar jelly.
C: The hormone cannot pass through glass, so the shoot remains
growing upright.
D: Light does not reach the tip of the shoot through the foil
cap, so the shoot continues to grow upright.
c)
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4 a) Plants respond to gravity and light (and some to
moisture).
b) They are relatively slow, and they are brought about by
growth and by chemical messages.
5 Because the roots must grow down into the ground as the seed
germinates, to absorb water and minerals and to anchor the
developing plant so it is not blown away. The roots must keep
growing down into the soil throughout the life of the plant. The
shoots must grow towards the light to get the maximum amount of
light energy onto the leaves, so they can photosynthesise and make
as much food as possible.
6 Use young bean seedlings, which normally grow straight up and
down. Attach some seedlings horizontally to a clinostat that is
slowly rotating vertically to make sure the effect of gravity is
felt equally all around the plant. Expect growth of both shoots and
roots to continue horizontally. Attach other seedlings horizontally
to a clinostat that is not rotating so that the seedlings are
affected by gravity on one side only. Expect the shoots to grow
upwards and the roots downwards, although the seedling is kept
horizontal.
Chapter 13: Reproduction in plants 1 asexually/sexually
sexually/asexually flowers pollinated wind brightly
coloured scent
2 a) Sexual: sex cells produced, fertilisation involved,
variation in offspring, good in a changing environment
Asexual: no sex cells produced, no fertilisation involved, no
variation in offspring, good in a stable environment
b) i) Asexual
ii) Runner
iii) Special stems emerge from the parent plant. A new small
plant forms on the end, which is identical to the parent plant.
Roots grow down into the soil and the runner drops away. This is a
form of asexual reproduction.
3 a) Runners come from the stems, and a new identical plant
forms where a runner touches the ground.
b) A piece of stem with few leaves is cut from a healthy plant,
put in damp compost or water until roots grow and then planted on
to become a full-sized plant (extra mark for mention of hormone
rooting powder). This is asexual reproduction because no sex cells
are produced, the new plant is identical to the parent plant,
etc.
4 propagator humid light cuttings transpiration
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5 a)
b) The transfer of pollen grains from the anther to the stigma,
either within the same flower (self-
pollination) or between different flowers
(cross-pollination)
c) By insects, because it has large, brightly coloured petals
and the sex organs are inside the petals
6 a)
b)
7 a) The joining of the male nucleus from the pollen with the
female nucleus in the ovule
b) B 1, D 2, E 3, C 4, A 5
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8 a) To avoid competition for nutrients, water, light, etc.,
between the parent plant and the offspring, and between the
seedlings.
b) Plums, which have a fleshy, sweet fruit, are eaten by
animals. The seeds pass through the animals body or are thrown
away.
Cockleburs have hooks that attach themselves to an animals coat.
The animal carries them along until it grooms itself and removes
the burs, or they fall off.
Maple seeds are dispersed by the wind. The wings allow them to
catch the wind and be blown quite a long way from the parent
tree.
9 a) A food store for the young plant as it germinates
b) The embryo root
c) The embryo shoot
d) The wall of the ovule which forms a tough, protective seed
coat
10 a) The seeds may drift down like parachutes, be shaped like
wings to catch the wind, or be very small and light.
b)
11 a) Warmth for efficient enzyme action, water for chemical
reactions to take place in solution and for hydrolysis reactions,
and oxygen for respiration
b) Any appropriate demonstration which shows awareness of the
need to control other variables, provide a control, etc.
12 We use rooting hormones in cuttings to make roots develop
reliably and quickly. We also use hormones to encourage the growth
of cells and then tiny plants in plant tissue cloning.
