Chapter 12.3 Cellular Pathogens✓

Question 1

Define a cellular pathogen

Answer 1

A living organism, either prokaryotic or eukaryotic, that can cause disease in a host

Question 2

What is the difference between a bacterium and bacteria?

Answer 2

-Bacterium is the singular term for a single prokaryotic cell
-Bacteria is the plural term referring to multiple cells

Question 3

List the structural features common to most bacteria

Answer 3

-Plasma membrane enclosed cytoplasm
-Ribosomes
-Single circular DNA (chromosome)
-Plasmid (small loops of DNA)
-Cell wall made of peptidoglycan
-Some have flagella for movement
-Some have a capsule for adhesion and virulence

Question 4

What is the function of a plasmid in bacteria?

Answer 4

-Plasmids are small loops of DNA that can be transferred between bacteria without affecting the bacterium’s basic functions.
-They may contain advantageous genes, such as those for antibiotic resistance or virulence factors

Question 5

What is the role of the bacterial capsule?

Answer 5

The capsule is thick, organised layer outside the cell that helps bacteria stick to surfaces and increases virulence by protecting against the immune system or antibiotics.

Question 6

Explain what an endospore s and why is it important

Answer 6

-An endospore is a dormant, tough structure formed by some bacteria that is resistant to extreme temperatures, chemicals and drying.
-It allows bacteria to survive unfavourable conditions and aids dispersal to new hosts

Question 7

Describe binary fission in bacteria

Answer 7

-Binary fission is an asexual reproductive process in which bacterium divided to produce two identical daughter cells.
-First, the bacterial DNA is replicated.
-Then, the cell elongates and splits into two, each daughter cell receiving a copy of the original DNA.

Question 8

Name the main shapes of bacteria and give the corresponding term for each

Answer 8

Spherical: Coccus (plural cocci)
Rod-shaped: Bacillus (plural bacilli)
Spiral: Spirillum (plural spirilla)
Comma-shaped: vibrio

Question 9

How can Gram staining help classify bacteria?

Answer 9

-Gram staining differentiates bacteria based on the structure and composition of their cell walls.
-Some bacteria retain the stain (Gram-positive) while other do not (Gram-negative) helping identify and classify them

Question 10

How can bacteria be grown in the laboratory?

Answer 10

-Bacteria can be grown by inoculating a small number of cells into a nutrient medium (liquid broth or sold agar).
-Cells divide to form colonies, which can be isolated and grown in pure culture for study

Question 11

Explain how bacteria causes disease in a host

Answer 11

-Once inside a host, bacteria divide rapidly.
-Some damage host tissues directly, while others produce toxins that disrupt cell function locally or systematically.
-Certain bacteria, like Mycobacterium Tuberculosis, can survive inside macrophages and multiply, evading the immune system.
-The pathogen multiplies while destroying host cells, leading to active infection and disease symptoms
-In plants, Agrobacterium tumefaciens inserts plasmid genes into host cells via wounds, causing tumour-like growths called galls that interfere with water and nutrient transport

Question 12

What is the main difference between how bacteria and viruses enter host cells?

Answer 12

-Viruses enter host cells via receptors-mediated endocytosis, while some bacteria can enter via phagocytosis by host immune cells like macrophages

Question 13

Give an example of a bacterial disease in humans and in plants including how each pathogen causes disease

Answer 13

Human
-Tuberculosis, caused by Mycobacterium tuberculosis, multiplies inside macrophages and damages lung tissue

Plant
-Crown gall, caused by Agrobacterium tumefaciens, inserts a plasmid gene into host cells, causing tumour-like galls and stunted growth

Question 14

What is the main difference between fungal cell walls and plant cell walls?

Answer 14

Fungal cell walls are made of chitin, whereas plant cell walls are made of cellulose

Question 15

Do fungi contain chlorophyll? Explain

Answer 15

No they do not contain chlorophyll so they cannot perform photosynthesis

Question 16

What is a hypha and what role does it play in fungi?

Answer 16

-A hypha is a long, thin filament of fungal cells.
-hyphae increase surface area for nutrient absorption and collectively form a mycelium, which is the main body of the fungus

Question 17

What is a mycelium?

Answer 17

A mycelium is an interwoven mass of hyphae that make up the body of a fungus and can infiltrate host tissue to obtain nutrients

Question 18

How do most fungi reproduce?

Answer 18

By producing spores, either sexually or asexually, from structures called sporangia

Question 19

Give an example of a fungal disease in animals and describe its impact

Answer 19

-Chytridiomycosis, caused by the amphibian chytrid fungus, infects frog skin
-The fungus produces spores that persists for years, aiding transmission and causing skin irritation and inflammation

Question 20

What are protists?

Answer 20

any member of a group of diverse eukaryotic, predominantly unicellular microscopic organisms.

Question 21

What structural features distinguish protists from bacteria?

Answer 21

-Protists are eukaryote with a membrane-bound nucleus and organelles, can be very small or up to 1 mm, and may reproduce sexually or asexually

Question 22

Compare Plasmodium and Phytophthora in terms of structure, movement and pathogenicity

Answer 22

-Plasmodium is an animal-like parasitic protist (protozoa) with no chlorophyll or cell wall.
-It spreads as sporozoites and cannot move independently, relying on host cells to infect.

-Phytophthora is a plant-like protist (oomycete) with cellulose-based cell walls and flagella for movement.
-It has a network of filaments for nutrient absorption and infect plant by penetrating root and phloem, producing large numbers of spores (zoospores) to transmit the pathogen

Question 23

What is a spore and why is it important for fungi and protists?

Answer 23

-A spore is a reproductive cell that forms without fertilisation.
-Spores allow fungi and some protists to survive unfavourable conditions, disperse to new hosts, and produce new organisms after germination

Question 24

Give an example of a protist that infects humans via contaminated water

Answer 24

-Giardia Lamblia is a flagellated protist that can caused intestinal illness when ingested in contaminated water

Question 25

Explain how Phytophthora cinnamomi infects plants and why is it harmful?

Answer 25

-Phytophthora cinnamomi infects plants by penetrating roots and extending into the phloem. -Its hyphae absorb nutrients, weakening the plant. -The pathogen produces spores that spread to new hosts. -Infection reduces nutrient and water transport, causing wilting, stunted growth and crop loss. -It is particularly destructive to Jarrah forests in Western Australia and Tasmania

Question 26

Recall the structural features eukaryotic pathogens have in common

Answer 26

-They are larger than prokaryotic pathogens. -They have membrane-bound organelles such as nuclei and mitochondria. -Their cells contain linear DNA packaged into chromosomes. -They may have specialised structures for movement (eg cilia, flagella, pseudopodia). -They usually reproduce sexually or asexually using mitosis/meiosis.

Question 27

Name and describe a plant disease caused by a protist agent

Answer 27

-One example is Phytophthora cinnamomi, a protist that causes dieback disease in Australian plants such as jarrah. -The protist infects the roots, preventing them from taking up water and nutrients. -This leads to wilting, yellowing leaves, reduced growth, and ultimately the death of the plant. -It has had major ecological impacts on forests and native flora.

Question 28

Describe the symptoms caused by Plasmodium Falciparum

Answer 28

-Recurrent fevers and chills due to cycles of parasite release from red blood cells. -Anaemia from destruction of red blood cells. -Weakness and fatigue. -In severe cases, cerebral malaria, seizures, coma, and organ failure.

Question 29

Distinguish between the structural features of fungi and protists

Answer 29

-Fungi: Have cell walls made of chitin, are mostly multicellular (except yeasts), absorb nutrients externally, and form thread-like structures called hyphae. -Protists: Do not have chitin cell walls (some have cellulose, some lack cell walls), are mostly unicellular, and often have locomotory structures such as cilia, flagella, or pseudopodia.

Question 30

Discuss the relationship between type of pathogen and type of symptoms

Answer 30

-The type of pathogen often determines the symptoms it produces, because symptoms usually arise from the pathogen’s method of infection and spread. For example: -Viruses damage host cells directly when they replicate inside and cause lysis, leading to symptoms such as fever, coughing, and tissue damage. -Bacteria often release toxins that cause inflammation, diarrhoea, or tissue necrosis. -Fungi may secrete digestive enzymes that break down host tissues, causing skin rashes, lesions, or rotting in plants. -Protists often damage cells by feeding directly on them or by triggering immune responses, leading to systemic symptoms such as fever or anaemia.

Question 31

Distinguish between the features of a fungal pathogen and a bacterial pathogen

Answer 31

Fungal pathogen -Eukaryotic -Chitin cell walls -Reproduces by spores -Often multicellular (hyphae). Bacterial pathogen -Prokaryotic, peptidoglycan cell walls -Reproduces by binary fission -Unicellular with no nucleus or membrane-bound organelles.

Question 32

Describe the difference between malaria and Plasmodium

Answer 32

-Plasmodium is the genus of protist parasite (eg Plasmodium falciparum). -Malaria is the disease caused by infection with Plasmodium.

Question 33

State three ways in which a bacterial pathogen can harm its host

Answer 33

-Releasing toxins (exotoxins or endotoxins). -Directly invading and damaging tissues. -Triggering harmful immune responses (eg inflammation).

Question 34

Describe the advantages of bacteria: a) Having a capsule b) Forming endospores/spores

Answer 34

a) Capsule -Protects bacteria from phagocytosis by immune cells -Helps them attach to surfaces -Prevents drying out. b)Endospores/spores -Allow bacteria to survive harsh conditions (heat, chemicals, desiccation) -Germinate when conditions improve.

Question 35

Describe the methods by which different stains of bacteria can be classified or identified

Answer 35

Bacteria can be classified and identified using several methods Gram staining: -Distinguishes Gram-positive (thick peptidoglycan wall) from Gram-negative (thin wall with outer membrane). Shape (morphology) -Cocci (spherical), bacilli (rod-shaped), spirilla (spiral). Growth requirements -Such as oxygen requirement (aerobic vs anaerobic). Biochemical tests -Enzyme activity, metabolic products, or nutrient use. Molecular techniques -DNA sequencing or PCR to identify genetic differences between strains.