4.3.3 Plant Diseases

Question 1

Plant diseases can be detected by:

Answer 1

Stunted growth
Spots on leaves
Areas of decay/rot
Growths
Malformed stems or leaves
Discolouration
The presence of pests

Question 2

How do aphids cause damage and how can they be controlled

Answer 2

Aphids (plant pests) feed on the sugary contents of the phloem by piercing the stems of plants with their sharp mouthparts. If the aphid burden is heave, the plant may not have sufficient sugar left for growth and will fail to thrive
Also make tiny holes which pathogens may enter through
Aphids can be controlled by chemical pesticides, or using biological control such as introduction of predators such as ladybirds

Question 3

Nitrate use in plants

Answer 3

Making amino acids, proteins, CHLOROPHYLL, DNA and many others

Question 4

Magnesium use in plants

Answer 4

Need to make chlorophyll

Question 5

Nitrate deficiency symptom

Answer 5

Stunted growth
Older leaves turn yellow

Question 6

Magnesium deficiency symptom

Answer 6

Chlorosis
Leaves turn yellow

Question 7

Plant defence responses

Answer 7

Physical barriers (designed to stop pathogens from getting inside plant cells/tissue): cellulose cell walls, tree bark, tough waxy cuticle on leaves

Chemical responses (chemical substance produced to deter organisms that might eat the plant): antibacterial chemicals, poisons

Mechanical adaptations (structural feats or responses): leaf droop/curl, thorns or hairs on stems, mimicry

Question 8

Plant defences: antibacterial chemicals

Answer 8

Chemical response
Some plants, e.g. witch hazel, produce chemicals that have antiseptic properties—killing microorganisms
Similar to:
Sebum, tears, HCl acid

Question 9

Plant defences: cellulose cell walls

Answer 9

A tough (but permeable to water) barrier that surrounds plant cells

Similar to:
Skin

Question 10

Plant defences: leaf droop/curl

Answer 10

Mechanical
When touched the leaves curl up quickly or can fl off. This can cause insects to fall off or give animals a fright, putting them off

Question 11

Plant defences: thorns or hairs on stems

Answer 11

Mechanical adaptation
These can make it painful for animals to eat the plant, or prevent insects from laying eggs on the plant
Similar to: cilia

Question 12

Plant defences: tree bark

Answer 12

Physical barrier
A layer of tough, dead cells surrounding the trunk and branches oof some plants
Similar to:
Scabs

Question 13

Plant defences: poisons

Answer 13

Chemical
Foxgloves and deadly nightshade contain chemicals that make animals feel unwell if eaten

Question 14

Plant defences: mimicry

Answer 14

Mechanical adaptation
Some plants mimic plants that are infected to prevent animals eating them or to prevents other insects from laying their eggs