4.16 Quiz: Plant Defenses against Pathogens

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Questions and Answers

What is the role of phenols like tannin in plants?

Promote herbivores feeding on the plant

Interfere with digestion to inhibit insect attacks (correct)

Encourage herbivores to attack the plant

Enhance digestion for insects

Which of the following is a function of alkaloids like caffeine and morphine?

Provide a bitter taste to prevent herbivores from feeding (correct)

Add a sweet flavor to deter herbivores

Repel pathogens by enhancing cell wall strength

Attract insects for pollination

What is the main function of defensins in organisms?

Break down the cell wall of invading organisms (correct)

Act as natural bacterial flora

Promote transport channels

Inhibit the flow of blood to infected areas

What is the primary cause of blight in potatoes?

Fungus Signup and view all the answers

What is one function of callose deposits in plant cells near the site of infection?

Strengthening the cell wall Signup and view all the answers

Which plant defense mechanism involves the thickening of cell walls with cellulose to prevent pathogen entry?

Lignin layer Signup and view all the answers

Which of the following is a primary non-specific defense mechanism in animals?

Competition of natural bacterial flora with pathogens Signup and view all the answers

How does inflammation contribute to the body's response to infection?

Increases blood flow and vessel permeability at infected sites Signup and view all the answers

Which term describes the necrosis of woody tissue in the main stem or branch of a plant?

Canker Signup and view all the answers

What are terpenoids that are produced by mint known for in terms of their properties?

Antibacterial properties Signup and view all the answers

Which type of plant tissue is blocked to prevent the spread of pathogens inside the plant?

Xylem Signup and view all the answers

What disease can potentially lead to death if the immune system becomes weakened?

Tuberculosis Signup and view all the answers

Which viral infection causes fevers, tiredness, and headaches as the first symptoms?

HIV Signup and view all the answers

How is Athlete's foot typically spread among humans?

By direct contact with spores on skin surfaces Signup and view all the answers

Which disease is transmitted via a vector in the form of a female Anopheles mosquito?

Malaria Signup and view all the answers

Which virus infects the ciliated epithelial cells of the gas exchange system?

Influenza Signup and view all the answers

What pathogen infects tobacco plants, causing disease in a major crop worldwide?

Virus Signup and view all the answers

Which of the following statements is true about bacteria?

Bacteria do not require a host to survive Signup and view all the answers

What is the main difference between bacteria and viruses in terms of genetic material?

Bacteria have DNA or RNA as genetic material Signup and view all the answers

What is responsible for the specificity of an antibody for a particular antigen?

Variable region with varying amino acid sequence Signup and view all the answers

Which component is present in bacteria but not in viruses?

Cell membrane Signup and view all the answers

What is the role of the immune system in response to Mycobacterium tuberculosis infection?

It seals infected phagocytes in tubercles Signup and view all the answers

In natural passive immunity, how do antibodies reach the baby?

Through the placenta and breast milk Signup and view all the answers

What stimulates the immune system to produce antibodies in active artificial immunity?

Vaccinations Signup and view all the answers

What characteristic makes viruses entirely dependent on their hosts?

Their inability to survive without a host Signup and view all the answers

How do antibiotics primarily fight infection?

By directly killing bacteria and halting their growth Signup and view all the answers

Which type of immunity results from the introduction of antibodies from another person or animal?

Passive immunity Signup and view all the answers

Why do most bacterial diseases show symptoms while TB can remain symptomless initially?

TB bacteria hide inside tubercles from the immune system Signup and view all the answers

What is crucial for the flexibility of antibody branches?

Hinge regions Signup and view all the answers

Study Notes

Pathogens

Bacteria and viruses are the main disease-causing pathogens in humans.
Bacteria are prokaryotic cells, lacking membrane-bound organelles and a nucleus, with genetic information stored in a circular strand of DNA.
Viruses consist of nucleic acid enclosed in a protein coat, with genetic material in the form of DNA or RNA.
Bacteria can survive without a host, whereas viruses are entirely dependent on their hosts.
Viruses are significantly smaller than bacteria.
Bacteria have cell membranes, cell walls, and cytoplasm, as well as organelles such as ribosomes, plasmids, flagellum, and pili, whereas viruses lack these structures.

Bacterial Diseases

Tuberculosis (TB) is caused by the bacterium Mycobacterium tuberculosis, which infects phagocytes in the lungs.
The first infection is symptomless, but the bacteria can become active again when the immune system is weakened, leading to breathing problems, coughing, weight loss, and fever.
Meningitis can be caused by bacterial infection of the meninges.

Viral Diseases

HIV (Human Immunodeficiency Virus) causes AIDS, with symptoms including fever, tiredness, and headaches.
After several weeks, HIV antibodies appear in the blood, making a person HIV positive.
Influenza is a viral disease that infects the ciliated epithelial cells of the gas exchange system, with different strains of the virus.

Diseases Caused by Other Organisms

Athlete's foot is caused by a fungus and is spread by direct contact with spores on the skin or other surfaces.
Malaria is an example of indirect transmission via a vector, in the form of a female Anopheles mosquito.

Plant Defences

Plants have evolved physical and chemical defences against pathogens.
Physical barriers include cellulose cell walls, a lignin layer, and waxy cuticles.
Old vascular tissue is blocked to prevent the spread of pathogens inside the plant.
Mechanisms to prevent the spread of infection include closing stomata, thickening cell walls with cellulose, and callose deposits.
Necrosis, or the killing of cells near the site of infection, is another mechanism to prevent the spread of infection.

Chemical Defences

Menthols, produced by mint, are terpenoids with antibacterial properties.
Phenols, such as tannin, interfere with digestion, preventing insects from attacking the plant.
Alkaloids, such as caffeine and morphine, have a bitter flavour, preventing herbivores from feeding on the plant.
Defensins are cysteine-rich proteins involved in inhibition of transport channels.
Hydrolytic enzymes, such as chitinases, are released to break down the cell wall of an invading organism.

Primary Non-Specific Defences in Animals

Physical barriers to infection include skin, stomach acid, and gut and skin flora.
Non-specific responses of the body to infection include inflammation, where histamines released by mast cells cause vasodilation and increase permeability of blood vessels.

Types of Immunity

Immunity can be active or passive.
Active immunity results from the production of antibodies by the immune system in response to an antigen.
Passive immunity results from the introduction of antibodies from another person or animal.
Natural active immunity arises from being exposed to an antigen or getting the disease.
Natural passive immunity is the result of crossing of mother's antibodies through the placenta and their presence in breast milk.
Active artificial immunity is acquired through vaccinations.
Passive artificial immunity is where antibodies are injected into the body.

Antibiotics

Antibiotics can be used to fight infection by killing bacteria and stopping their growth.

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Learn about how plants have evolved defenses against pathogens, such as physical barriers like cellulose cell walls and chemical defenses. Discover how plants combat diseases like blight in potatoes and Black Sigatoka in bananas.

Plant Defenses against Pathogens

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