plant diseases

Question 1

What are antibacterial chemicals?

Answer 1

Naturally occurring chemicals made by plants like mint and witch hazel which protect them from bacterial pathogens

Question 2

bacteria

definition

Answer 2

Single-celled microorganisms, some of which are pathogenic in humans, animals and plants. Singular is bacterium

Question 3

biodiversity

meaning

Answer 3

The range of animals and plants in a given area

Question 4

cellulose

definition

Answer 4

A carbohydrate. It forms the cell wall in plant cells.

Question 5

communicable disease

definition

Answer 5

A disease that is caused by a pathogen and so is transmitted rather than inherited or caused by an environmental factor.

Question 6

cuticle

definition

Answer 6

The outer layer of a leaf which protects it.

Question 7

fungi

definition

Answer 7

A large group of eukaryotic organisms that contain single celled yeasts, moulds and mushrooms.

Question 8

genetic engineering

definition

Answer 8

Process which involves the artificial transfer of genetic information from one donor cell or organism to another.

Question 9

herbivore

definition

Answer 9

An animal that feeds only on plants

Question 10

host

definiton

Answer 10

The organism lived on or in by a parasite.

Question 11

pathogen
definition (basic)

Answer 11

Microorganism that causes disease.

Question 12

protist

definition

Answer 12

A eukaryotic, usually single-celled organism of the kingdom Protista.

Question 13

transmission

meaning

Answer 13

The spreading of pathogenic disease, for example by touch, food, water.

Question 14

What are viruses?

Answer 14

Ultramicroscopic non-cellular organisms that replicate themselves inside the cells of living hosts.

Question 15

Pathogen
definition (detailed)

Answer 15

A pathogen is an organism that causes a disease. There are four main types of pathogen: viruses, bacteria, fungi, and protists. All types of pathogen have a simple life cycle. They infect a host, reproduce (or replicate themselves if a virus), spread from their host and then infect other organisms.

Question 16

What are the 4 main types of pathogen?

Answer 16

• Viruses
• Bacteria
• Fungi
• Protists

Question 17

Effects of plant pathogens

Answer 17

Plant pathogens kill or reduce the growth of many plants, which in turn can reduce biodiversity.

Question 18

Identification of pathogens
Scientists want to identify potential plant pathogens as quickly as possible to reduce the likelihood of an infection spreading. The process to identify a disease may include the following steps:

Answer 18

1) Following a report of a possible infection, scientists will visit the location.
2) To avoid any confusion it is essential they look at other factors that might cause similar symptoms. For example, damage to leaves might be caused by a pathogen or grazing animals.
3) The scientists will try to identify any environmental causes such as pollution that might be affecting the plants.
4) Finally they will photograph the symptoms and take samples for laboratory analysis.

Question 19

Identification of pathogens
Scientists want to identify potential plant pathogens as quickly as possible to reduce the likelihood of an infection spreading.

What is the next step after identifying the infection?

Answer 19

Once an infection has been identified, scientists will look for any patterns in the distribution of infected plants. Do they all appear downwind of the first infection? Are future cases reported along the banks of rivers and streams?

Question 20

Identification of pathogens

Symptoms of plant disease

Answer 20

Plant pathogens cause diseases with a range of different symptoms. These symptoms can be used to identify the pathogen and then treat the disease, or limit its effects.

Pests can also cause damage to plants. Examples are the insects, aphids and mealybugs. Although these do not cause disease, as pathogens do, they can weaken and damage the plant. It is important to identify which pests are causing symptoms, as well as identifying which pathogen is causing a disease, so that the correct treatment can be decided.

Question 21

Identification of pathogens
Symptoms of plant disease
Give 6 examples of symptoms of common plant infection.

Answer 21

• Stunted growth from mealybugs: Mealybugs can cause dehydrated plants which are likely to have stunted growth
• (Black and purple) Spots on leaves caused by the rose black spot fungus
• Decay caused by the rice blast fungus
• Malformed stems or leaves caused by the ash dieback fungus
• Discoloration caused by the tobacco mosaic virus
• The presence of pests (aphids): Aphid insects suck sap from a nettle

Question 22

Identification of pathogens

Answer 22

Farmers and gardeners often use books like gardening manuals and the internet to identify plant diseases. They do this by comparing the symptoms of their plants with images of other infected ones. Gardeners can also take a small cutting of an infected plant (or a photograph of it) to a local garden centre. Here staff can help identify the disease by looking at its symptoms. Gardeners can then buy suitable treatments from the garden centre to treat the disease.

Question 23

Plant defences
(overview)

Answer 23

Plants are constantly defending themselves from attack from pests and pathogens. Like animals, plants have physical and chemical defences which help to prevent infection and disease.

Question 24

Plant defences

List Physical defences

Answer 24

• Bark
• Thorns and hairs
• Drooping leaves

Question 25

Plant defences
Physical defences

Bark

Answer 25

Many plants are covered with a thick bark. This is an external layer of dead cells which forms a physical barrier against infection. In this way it is very much like our skin. Leaves are covered with waxy cuticle which also helps to prevent their cells from becoming infected

Beyond bark and the waxy cuticle, each plant cell has a cellulose cell wall which acts as another barrier against infection. Some pathogens overcome this barrier by releasing enzymes that soften the cell wall.

Question 26

Plant defences
Physical defences

Thorns and hairs

Answer 26

Plants like roses have evolved large thorns to avoid being eaten, while plants like cacti have evolved thin spines. These adaptations protect plants from damage from pests and from disease from pathogens carried by pests.

Question 27

Plant defences
Physical defences

Drooping leaves

Answer 27

The Mimosa pudica plant is very special. It has evolved to close its leaves and then point its stems towards the ground when touched by an insect as it lands on it. This movement is a defence mechanism which acts to dislodge any insect that rests on it. You can see this happen below.

Question 28

Plant defences
Chemical defences

Why, as opposed to physical?

Answer 28

Sometimes physical defences are not enough to protect a plant. Physical barriers alone will often not be enough of a deterrent against plant eating pests for example.

Question 29

Plant defences
Chemical defences

poisons

Answer 29

Some plants, like stinging nettles and foxgloves, have developed poisons to deter herbivores from eating them. They produce these constantly. These do not defend plants from infection by pathogens.

Question 30

Plant defences
Chemical defences

Toxins

Answer 30

Other plants produce toxins in response to being attacked, for example, some plants release a toxin into the air when attacked by aphids. This toxin acts as a warning to other aphids, causing them to fly away.

Question 31

Plant defences
Chemical defences

antibacterial chemicals

Answer 31

As a way of defending themselves against pathogens, some plants such as mint and witch hazel produce antibacterial chemicals. These kill bacteria that were not stopped by physical defences. We now use these chemical defences in antiseptics for humans.

Question 32

Plant defences

Defences other than physical and chemical

Answer 32

Farmers can now genetically engineer crop plants to be resistant to infections.

Question 33

Plant defences

What type of pathogen is Chalara ash dieback?

Answer 33

Fungus

Question 34

Plant defences

What plants are aphids often found on?

Answer 34

Roses