plant responses to herbivory (a)

Question 1

What are tannins?

Answer 1

• phenols
• very bitter taste = puts animals off eating the leaves
• toxic to insects - they bind to digestive enzymes produced in the saliva and inactivate them
• e.g. tea and red wine are rich in plant tannins

Question 2

What are alkaloids?

Answer 2

• large group of very bitter tasting, nitrogenous compounds
• many act like drugs, affecting an animals metabolism and can poison them
• e.g. caffeine, nicotine, morphine, cocaine
• caffeine = toxic to fungi and insects - (in coffee bush seedlings) can be spread through soil and prevent the germination of seeds of other plants
• nicotine = toxin produced in the roots of tobacco plants, transported to the leaves + stored in vacuoles to be released when leaf is eaten

Question 3

What are terpenoids?

Answer 3

• often form essential oils but act as toxins to fungi and insects that might attack
• can interfere with the nervous system or act as insect repellents

Question 4

What are pheromones?

Answer 4

• chemicals affecting the social behaviour of other members of the same species
• e.g. in plants they can communicate by chemicals in root systems to ‘tell’ other plants that it is under water stress
• VOCs - volatile organic compounds - act like -pheromones - diffuse through air in and around plant. usually made the plant detects attack by an insect pest through chemicals in the saliva of the insect which may elicit gene switching

Question 5

Folding in response to touch

Answer 5

• the sensitive plant Mimosa pudica uses conventional defences against herbivores - it contains a toxic alkaloid and the stem has sharp prickles
• moves at a fast speed
• if leaves are touched, they fold down and collapse to frighten larger herbivores and dislodge insects
• leaf recovers in 10-12 mins due to potassium ion movement into specific cells, followed by osmotic water movement