(Paper 1) 3.4 Disease: Plant diseases

Question 1

Why are plant diseases a serious issue for ecosystems and humans?

Answer 1

They can kill or stunt plants, reducing biodiversity and food supply (e.g. the Irish potato famine).

Question 2

What was the cause of the Irish potato famine?

Answer 2

A pathogen that caused blight, rotting the potato tubers and making them inedible.

Question 3

What type of organism causes tobacco mosaic virus?

Answer 3

A virus.

Question 4

What does TMV do to leaves?

Answer 4

Causes a mosaic pattern of yellow/white, chlorosis, crinkling or curling of leaves.

Question 5

How does TMV affect the plant’s health?

Answer 5

It reduces photosynthesis, lowering growth and crop yields.

Question 6

How is TMV transmitted?

Answer 6

Through direct contact between plants or via farmers’ hands.

Question 7

Is there a cure for TMV?

Answer 7

No – farmers must prevent infection and limit its spread.

Question 8

What are symptoms of rose black spot?

Answer 8

Black or purple spots on leaves, which then turn yellow and drop off.

Question 9

What effect does rose black spot have on the plant?

Answer 9

Reduces photosynthesis and growth.

Question 10

How is rose black spot transmitted?

Answer 10

By air, water, or direct contact (e.g. by gardeners).

Question 11

How is rose black spot treated?

Answer 11

Using fungicides and removing infected leaves.

Question 12

What are aphids?

Answer 12

Insects that infest plants and suck sap from new shoots.

Question 13

What is the effect of aphids on plants?

Answer 13

They reduce growth and can kill the plant.

Question 14

What is a natural predator of aphids?

Answer 14

Ladybirds, which gardeners use to reduce aphid numbers naturally.

Question 15

What is a deficiency disease in plants?

Answer 15

A disease caused by a lack of essential mineral ions needed for healthy growth.

Question 16

Why are mineral ions important for plants?

Answer 16

They are needed for photosynthesis, protein synthesis, and overall healthy growth.

Question 17

What are nitrates used for in plants?

Answer 17

To make proteins, which are needed for growth.

Question 18

What are the symptoms of nitrate deficiency?

Answer 18

Reduced chlorophyll

Leaves turn pale green or yellow (chlorosis)

Stunted growth

Question 19

How do plants absorb nitrates?

Answer 19

Through their roots, from water in the soil.

Question 20

How can nitrate deficiency be treated?

Answer 20

By applying fertilisers or manure to the soil.

Question 21

What is magnesium used for in plants?

Answer 21

To make chlorophyll, needed for photosynthesis.

Question 22

What are the symptoms of magnesium deficiency?

Answer 22

Chlorosis (yellowing of leaves)

Reduced photosynthesis

Poor growth

Question 23

Why is magnesium called a limiting factor in growth?

Answer 23

Because lack of magnesium reduces chlorophyll, limiting photosynthesis and growth.

Question 24

Why are seedlings grown without nitrogen smaller?

Answer 24

Nitrogen is needed to make proteins, which are used for growth and repair.

Question 25

What is nitrogen used for in plants?

Answer 25

To make proteins.

Question 26

Why do seedlings grown without magnesium appear yellow and small?

Answer 26

Magnesium is needed to make chlorophyll, which is essential for photosynthesis.

Question 27

What is chlorosis?

Answer 27

Yellowing of leaves, often caused by magnesium deficiency.

Question 28

Why does lack of magnesium lead to poor growth?

Answer 28

Without chlorophyll, photosynthesis is reduced, so the plant has less energy for growth.

Question 29

What do plants defend themselves against?

Answer 29

Pathogens and herbivores.

Question 30

What are the two main types of plant defences?

Answer 30

Physical and chemical defences.

Question 31

What is the function of bark in plants?

Answer 31

Acts like skin – a physical barrier made of dead cells to block pathogens.

Question 32

What is the function of the cell wall in plant cells?

Answer 32

The cellulose wall provides a physical barrier to infection.

Question 33

What is the waxy cuticle and what does it do?

Answer 33

A protective layer on leaves that prevents infection and water loss.

Question 34

What do some plants like mint and witch hazel produce?

Answer 34

Antibacterial chemicals to limit the spread of pathogens.

Question 35

How are plant-produced antibacterial chemicals useful to humans?

Answer 35

They are used in antiseptics.

Question 36

Why do some plants like stinging nettles produce poisons?

Answer 36

To defend against herbivores, not pathogens.

Question 37

How can farmers improve plant disease resistance?

Answer 37

By using genetic engineering to make crops resistant to infections.

Question 38

What are mechanical defences in plants?

Answer 38

Structural or behavioural adaptations that help deter herbivores from eating them.

Question 39

Why do plants need mechanical defences?

Answer 39

To protect themselves from being eaten by herbivores or damaged.

Question 40

What is the purpose of thorns and hairs on plants?

Answer 40

To prevent herbivores from feeding or damaging the plant (e.g. roses and cacti).

Question 41

What unique defence does the Mimosa pudica plant use?

Answer 41

It droops its leaves and stems downward when touched, deterring insects from feeding.

Question 42

What is mimicry in plants?

Answer 42

When a plant imitates something else in its environment to avoid harm.

Question 43

How does the passion flower vine use mimicry?

Answer 43

It has yellow spots that resemble butterfly eggs, discouraging real butterflies from laying eggs.

Question 44

How does mimicry benefit the passion flower vine?

Answer 44

Fewer caterpillars hatch and feed, so the plant suffers less leaf damage.