Stage 9 · Unit 2 Plant Biology
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Secondary 2 · Science · Unit 2

Science Unit Test 2
Plant Biology

Photosynthesis · Chlorophyll · Minerals · Investigations
38 questions · self-marked · 49 marks
UNIT TEST 2 · WHAT TO REVISE
Scope: Unit 2 — Plant Biology. Everything on this sheet is testable: what photosynthesis is and its word equation, chloroplasts and chlorophyll, what the plant does with its glucose, energy stores, magnesium and nitrate, fertilisers, and the two class investigations (light intensity & the starch test).

📺 Watch & Learn first

Stuck? Watch a short video, then come back and try the questions. The two marked Unit 2 slides are the ones linked from the lesson slides; the rest follow the order of the sections below.

FuseSchool · What Is Photosynthesis? FuseSchool · Structure Of The Leaf FuseSchool · Plant Nutrition (Unit 2 slides) Garden Tips · Leaf Yellowing & Nutrient Deficiency (Unit 2 slides) FuseSchool · Factors Affecting the Rate of Photosynthesis Science4Breakfast · Testing a Leaf for Starch Using Iodine More videos →
🌞 A · Photosynthesis 🍃 B · Chlorophyll & Glucose 🌱 C · Minerals & Growth 🔬 D · Investigations
🌞
Section A

Photosynthesis

Photosynthesis is the process by which plants use sunlight, water and carbon dioxide to make oxygen and energy in the form of a sugar, glucose. Plants are called producers because they produce their own food. Water comes from the soil through the roots; carbon dioxide comes from the air. Oxygen is released into the atmosphere and glucose is used for biomass and energy.
What goes in and what comes out of a leaf
Light is the energy source — it is neither a reactant nor a product.
light energy
carbon dioxide + water  →  glucose + oxygen
(chlorophyll)
Q1
A leafy plant is sealed in a clear jar and left in bright light. Over the next hour the carbon dioxide in the jar falls and the oxygen rises. Which process explains this?
1 mark
Respiration
Photosynthesis
Transpiration
Mineral absorption
Q2
Plants are called producers. Why?
1 mark
They produce the minerals found in the soil
They eat other organisms to get their energy
They produce more offspring than animals do
They produce their own food, using sunlight as the energy source
Q3
A student fills in the “what goes in / what comes out” table for a leaf, but writes glucose in the “goes in” column. What is wrong with that?
1 mark
Glucose is what the leaf builds, not something it takes in
Nothing — the roots absorb glucose from the soil
Glucose belongs in both columns, since it is taken in and given out
Glucose is a mineral, so it needs a column of its own
Q4
Which pair are the products of photosynthesis?
1 mark
Carbon dioxide and water
Water and minerals
Glucose and oxygen
Chlorophyll and starch
Q5
In the “what goes where?” sorting activity, light was not placed with the reactants or with the products. Why not?
2 marks
Light is a product that plants only make at night
Light is a mineral that is absorbed by the roots
Light is both a reactant and a product at the same time
Light is not a substance — it is the energy source that drives the reaction
Q6
A gardener accidentally cuts through most of a plant’s roots. Which raw material for photosynthesis will the plant now struggle to obtain?
1 mark
Carbon dioxide
Water
Sunlight
Glucose
Q7
Where does a plant get the carbon dioxide it uses in photosynthesis?
1 mark
From the air
From the soil, through its roots
From the water it absorbs
From the minerals in fertiliser
Q8
A student writes glucose + oxygen → carbon dioxide + water and labels it “photosynthesis”. What has gone wrong?
2 marks
Nothing — that is the correct equation
The equation is right, but light energy belongs on the left with the reactants
They have written it the wrong way round — that is respiration
They should have written minerals in place of oxygen
Q9
Photosynthesis matters to every living thing, for two main reasons. Select both.
2 marks
Select 2 · both must be right for the marks
It provides energy, stored as chemical energy in nutrients, for almost all other organisms
It removes all bacteria from the soil
It provides the oxygen in the Earth’s atmosphere
It makes the minerals that plants absorb through their roots
PHOTOSYNTHESIS — SECTION SCORE
0/12
🍃
Section B

Chlorophyll & What Glucose Is Used For

A chloroplast is an organelle found only in plant cells — it is where photosynthesis happens. Chlorophyll is the green pigment inside the chloroplast that captures energy from sunlight. Plants use the glucose they make for respiration, making cellulose for cell walls, making starch stores, making proteins for growth and repair, and making fats and oils for storage. Extra carbohydrate is stored as starch inside the chloroplasts. Roots and tubers store starch/glucose; nuts and seeds store fats and oils.
Q10
In which organelle does photosynthesis take place?
1 mark
The nucleus
The cell wall
The cell membrane
The chloroplast
Q11
What is the difference between a chloroplast and chlorophyll?
1 mark
They are two words for exactly the same thing
The chloroplast is the organelle where photosynthesis happens; chlorophyll is the green pigment inside it that absorbs sunlight
Chlorophyll is the organelle; the chloroplast is the green pigment inside it
The chloroplast is found in animal cells and chlorophyll in plant cells
Q12
Name the green pigment that captures energy from sunlight. (Type your answer.)
1 mark
Q13
A student says: “Plants photosynthesise but they can also respire. This means they can make food even when there is no sunlight.” What is wrong with this?
1 mark
Nothing — the statement is completely correct
Plants do not respire at all, only animals do
Plants do respire, but without sunlight they cannot photosynthesise, so they stop making glucose
Plants only respire at night and never photosynthesise
Q14
Which of these is not something a plant uses its glucose for?
1 mark
Absorbing minerals from the soil
Making cellulose for cell walls
Respiration
Making starch stores
Q15
Select all four things a plant uses the glucose made in photosynthesis for.
3 marks
Select 4 · all four must be right for the marks
Respiration
Making cellulose for cell walls
Making light energy to shine on the leaf
Making starch stores
Making fats and oils for storage
Making the magnesium it needs for chlorophyll
Q16
Nuts and seeds are energy stores. What do they mainly store?
1 mark
Nitrates from the soil
Starch and glucose
Chlorophyll
Fats and oils
Q17
Tubers and roots (for example a potato) are stores of:
1 mark
Fats and oils
Chlorophyll
Starch and glucose
Carbon dioxide
Q18
Where inside a leaf cell is the starch stored?
1 mark
In the cell wall
Inside the chloroplasts
In the nucleus
In the soil around the roots
Q19
On a warm, sunny day, why does a plant turn some of its carbohydrate into starch?
2 marks
Because it makes more carbohydrate than it needs immediately, and stores some for later — at night, or at a time of year with less sunlight
Because starch attracts more sunlight to the leaf than glucose does
Because starch is a mineral the plant cannot get from the soil
Because glucose cannot be used in respiration
CHLOROPHYLL & GLUCOSE — SECTION SCORE
0/13
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Section C

Minerals & Plant Growth

Minerals are water-soluble substances that plants absorb from the soil through their roots. Plants need only small quantities, but if the soil runs short the plant cannot grow to its full potential. Fertilisers contain minerals, which is why adding them raises the yield — the quantity of crop harvested. Two important minerals are magnesium and nitrate.
MAGNESIUM · Mg

Needed to make chlorophyll

Too little magnesium → not enough chlorophyll → leaves look yellow instead of green, less light energy is absorbed, and the plant photosynthesises less than it should.

NITRATE · contains N

Needed to make proteins

Nitrogen lets the plant convert carbohydrates into proteins, which are essential for making new cells. Too little nitrogen → the plant grows slowly and stays small, leaves are pale and may die. Nitrogen is also needed for chlorophyll.

Q20
What are minerals, and how does a plant get them?
1 mark
Fats, stored in the seeds
Gases, absorbed from the air through the leaves
Sugars, made inside the chloroplasts
Water-soluble substances, absorbed from the soil through the roots
Q21
Which mineral does a plant need in order to make chlorophyll? (Type the name or its symbol.)
1 mark
Q22
A plant that is short of magnesium has leaves that look:
1 mark
Darker green than usual
Yellow (or brown) instead of green
Bright blue
Completely unchanged
Q23
Explain the chain: why does a magnesium-deficient plant grow badly?
2 marks
Because magnesium is the main gas used up in photosynthesis
Because magnesium is what plants convert into proteins for new cells
Without magnesium it cannot make enough chlorophyll, so it absorbs less energy from sunlight and photosynthesises less than it should
Because magnesium is what keeps the soil moist around the roots
Q24
Nitrate contains nitrogen atoms. What does a plant mainly need nitrogen for?
1 mark
Converting carbohydrates into proteins
Making the cell wall waterproof
Absorbing carbon dioxide from the air
Storing fats and oils in the seeds
Q25
Why do proteins matter so much for a plant’s growth?
1 mark
Proteins are released from the leaf as a waste gas
Proteins are the plant’s main store of fats and oils
Proteins absorb sunlight instead of chlorophyll
Proteins are essential for making new cells
Q26
What happens to a plant, such as maize, that does not get enough nitrogen?
1 mark
It grows very tall, very quickly
Its leaves turn a much darker green
It grows slowly and stays small, and its leaves are pale and may die
It stops absorbing water through its roots
Q27
Match the description to the mineral: “The plant cannot make proteins, so growth is slow and the leaves are pale.”
1 mark
Magnesium
Nitrogen
Oxygen
Carbon
Q28
Why do farmers add fertiliser to a field of wheat?
1 mark
Fertiliser contains minerals the soil may be short of, so crops grow larger and give a higher yield
Fertiliser replaces sunlight on cloudy days
Fertiliser supplies the carbon dioxide the crop needs
Fertiliser stops the crop from respiring, saving its energy
Q29
How can a farmer work out where in a field fertiliser is actually needed?
1 mark
By counting how many leaves each plant has
By spreading exactly the same amount everywhere
By measuring the air temperature above the crop
By testing the soil in different parts of the field to see which minerals are lacking
Q30
Legumes — beans, peanuts and soy — flourish even on nitrogen-deficient soils. Why?
2 marks
They have no need for nitrogen at all
They make their own nitrate inside their chloroplasts
With help from Rhizobium bacteria they can fix nitrogen from the air
They use magnesium in place of nitrogen
MINERALS & PLANT GROWTH — SECTION SCORE
0/13
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Section D

Think Like a Scientist — Investigations

Two investigations from Unit 2. (1) Light intensity and the rate of photosynthesis: pondweed under water gives off bubbles of oxygen; count the bubbles per minute as you move a lamp closer or further away. (2) Testing a leaf for starch: a leaf that has been photosynthesising has stored starch, which turns iodine solution blue-black.
Typical results: bubbles per minute against light intensity
The curve rises, then levels off — something other than light has become the limit.
Q31
In the pondweed investigation, how is the rate of photosynthesis measured?
1 mark
By weighing the lamp
By counting the bubbles of gas given off each minute
By measuring how long the pondweed is
By counting how many leaves the pondweed has
Q32
Which gas is inside those bubbles? (Type your answer.)
1 mark
Q33
How is the light intensity changed during the investigation?
1 mark
By moving the lamp closer to, or further from, the pondweed
By warming the water with a heater
By adding fertiliser to the water
By swapping in a different species of pondweed each time
Q34
Look at the graph above. The line rises at first, then levels off. What does the flat part show?
2 marks
The pondweed has died
The light intensity has started to fall again
The pondweed has switched from photosynthesis to respiration
Extra light no longer speeds things up, because something else — such as carbon dioxide or temperature — is now the limit
Q35
Which of these must be kept the same throughout the investigation, so the test is fair?
1 mark
The distance from the lamp to the pondweed
The number of bubbles counted
The temperature of the water
The brightness reaching the pondweed
Q36
A leaf is tested for starch with iodine solution. What is a positive result?
2 marks
The iodine turns completely colourless
The iodine turns blue-black
The leaf turns bright green again
The leaf starts giving off bubbles
Q37
Before adding the iodine, the leaf is boiled in ethanol. Why?
1 mark
To remove the green chlorophyll, so the colour change can actually be seen
To add extra starch to the leaf
To make the leaf photosynthesise faster
To turn the glucose in the leaf into starch
Q38
Why does testing a leaf for starch tell you whether that leaf has been photosynthesising?
2 marks
Because starch is a reactant that photosynthesis uses up, so less starch means more photosynthesis
Because chlorophyll turns into starch whenever the leaf is left in the dark
Because the glucose made in photosynthesis is stored as starch in the leaf, so starch being present means photosynthesis has happened
Because starch is absorbed from the soil, but only while the leaf is in the light
INVESTIGATIONS — SECTION SCORE
0/11
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