Unit 3 KA3

Question 1

Monoculture

Answer 1

Huge numbers of a single species of crop plant grown over a wide area to improve efficiency.

Monocultures are vulnerable to attacks by diseases or insect pests, which can spread rapidly.

Question 2

Weed

Answer 2

Any plant growing where it is not wanted.

Competes with the crop for light, nutrients and water, reducing productivity.

May release chemical inhibitors into the soil, act as hosts for crop pests and diseases and contaminate crops with their seeds.

Question 3

Annual weeds

Answer 3

Complete their life cycle in one year.

Grow and produce flowers rapidly, produce large numbers of seeds that can remain dormant in the soil for a long time.

eg. poppies, Arabidopsis (Thale cress - model organism)

Question 4

Perennial weeds

Answer 4

Live for several years, becoming dormant in the winter and re-growing in the spring.

Compete with crops as they are already established in the habitat.

Have food storage organs such as deep tap roots. eg. dandelions

Reproduce vegetatively (asexually) using runners eg. buttercups, or rhizomes (underground stems) eg couch grass

Question 5

Invertebrate pests

Answer 5

Invertebrates are animals without backbones.

Invertebrate pests include insects, especially larval stages of butterflies (caterpillars) and aphids; molluscs (slugs and snails) and nematode worms.

Question 6

Leaf damage by pests

Answer 6

Caterpillars and molluscs eat leaves, reducing photosynthesis and therefore production of sugars for growth and starch storage.

Question 7

Effect of aphids (greenfly)

Answer 7

Pierce the phloem to suck out the sucrose, reducing productivity and transmitting viruses.

Question 8

Effect of nematodes

Answer 8

Attack roots and tubers, laying eggs inside them.

They damage crops and make them unmarketable, due to their appearance.

Question 9

Plant diseases

Answer 9

Caused by pathogens such as fungi, viruses and bacteria.

They are carried in the soil, are airborne or are transmitted by insect pests such as aphids.

They reduce crop yield and productivity, make products less marketable due to their appearance and reduce storage life.

eg. potato blight, apple scab

Question 10

Cultural control - definition

Answer 10

Use of traditional methods to controlling pests and diseases.

Usually preventative and involve planning.

Question 11

Ploughing

Answer 11

Turning over the top layers of the soil to bury weeds.

Question 12

Timing of sowing and weeding

Answer 12

Allows crops to outcompete weeds.

Question 13

Removal of alternative hosts and crop residues

Answer 13

Reduces habitats for pests and sources of fungal spores.

Question 14

Cover crops

Answer 14

Example - clover (N-fixer)

Used to enrich the soils and prevent weeds from becoming established.

Good for pollinators.

Question 15

Crop rotation

Answer 15

Growing crops in a different location each year to break pest lifecycles.

Question 16

Pesticides

Answer 16

Chemicals used to control pests and diseases.

Include herbicides, pesticides and fungicides.

Question 17

Selective herbicides

Answer 17

Used to kill broad leaved weeds that compete with grass and cereal crops (narrow leaved).

Similar to plant hormones and work by over-stimulating growth so that the weeds exhaust their food reserves and die.

Non-toxic and biodegradable.

Question 18

Contact herbicides

Answer 18

Non-selective.

Kill all green plant tissue that they come into contact with rapidly.

Biodegradable with short-lived effects.

Do not affect underground storage organs.

Question 19

Systemic herbicides

Answer 19

Absorbed by weeds and transported internally to other parts via the phloem.

Act slowly, but are more effective as they reach roots and underground storage organs.

Question 20

Other pesticides

Answer 20

Chemicals used to kill invertebrate pests - insecticides, mollluscicides and nematocides.

(The term also refers to herbicides and fungicides)

Question 21

Contact pesticides

Answer 21

Kill the pest when it is sprayed, and remain as a protective layer on the crop plant, as a poisonous residue.

Question 22

Systemic pesticides

Answer 22

Absorbed by the plant and are transported to all parts via the phloem.

When the plant is attacked (eg. when the phloem is pierced by an aphid) the toxin is ingested, killing the pest.

Question 23

Fungicides

Answer 23

Pesticides that kill fungal parasites on crop plants, eg. potato blight.

Question 24

Contact fungicides

Answer 24

Sprayed onto the crop before the spores land, as a protective layer.

Spores are killed as they germinate.

Easily washed off, so repeat applications needed.

Question 25

Systemic fungicides

Answer 25

Absorbed and transported by the crop plant.

Fungi are killed when the spores germinate and penetrate the tissue of the plant.

Give longer lasting protection.

Question 26

Blight forecast

Answer 26

Weather data is used to alert farmers to spray their crop, as a preventative measure, when weather conditions are ideal for fungal growth - warm and humid.

Saves unnecessary spraying and is more effective than treating an established fungal infection.

Question 27

Characteristics of an ideal pesticide

Answer 27

Safe

Effective

Non-toxic (to non-target species)

Specific

Biodegradable

Question 28

Pesticide persistence

Answer 28

Pesticides such as DDT are harmless at low concentrations, but persist in the environment as they are non-biodegradable.

Question 29

Bioaccumulation

Answer 29

The build up of a pesticide in the tissues of a living organism.

Question 30

Biomagnification

Answer 30

The increase in the concentration of a chemical moving between trophic levels.

Tertiary consumers (such as birds of prey) can be badly affected by biomagnification.

Question 31

Pesticide resistance

Answer 31

The application of pesticide acts as a selection pressure on variation within a pest population.

Resistant individuals survive, breed and pass on their alleles for resistance to the next generation.

These alleles therefore increase in frequency.

This is an example of natural selection, resulting in high speed evolution.

Question 32

Biological control

Answer 32

The control of a pest using a parasite, predator or pathogen.

Pests are not eliminated, but their population is kept at a low level.

eg. use ladybirds to control aphids, Encarsia (parasitic wasp) to control whitefly

Question 33

Benefits of biological control

Answer 33

Reduces pesticide use

Highly specific

Less chance of resistance developing.

Works well in controlled conditions, eg. glasshouses.

Question 34

Problems with biological control

Answer 34

The biological control agent may become an invasive species, eg. Cane toads in Australia

Question 35

Integrated pest management (IPM)

Answer 35

A combination of chemical control, biological control, cultural methods and crop resistance (could be natural or GM resistance, eg. Bt toxin).

Reduces use of pesticides and brings pest populations down to a manageable level, without eliminating them.

Aims to control the target species, whilst reducing harm to the environment - a more sustainable approach.