SCSA Biology Homeostasis
5 sample questions with marking guides and sample answers · Avg. score: 84%
To reduce water loss, xerophytes often have
extensive root systems.
While extensive root systems help xerophytes maximize water absorption from deep or widespread soil areas, they do not function to reduce water loss.
large numbers of root hairs.
Large numbers of root hairs increase the surface area for water absorption from the soil, but they do not play a role in preventing water loss.
leaves with thick cuticles.
A thick waxy cuticle on the epidermis of leaves creates a waterproof barrier that significantly reduces water loss through transpiration.
large flat leaves.
Large flat leaves would increase the surface area exposed to the sun and air, which would actually increase water loss through transpiration rather than reduce it.
Which of the following is an example of a physiological adaptation in a plant?
closing stomata during the day
This is correct because the active opening and closing of stomata is an internal, functional process (often used by CAM plants to conserve water), which defines a physiological adaptation.
stomata located in pits
This is incorrect because the physical location of stomata in sunken pits is a permanent anatomical feature, making it a structural adaptation rather than a physiological process.
stomata surrounded by hairs
This is incorrect because the presence of leaf hairs (trichomes) is a physical characteristic built into the plant's anatomy, which is a structural adaptation.
fewer stomata on upper leaf
This is incorrect because the distribution and quantity of stomata on a leaf are permanent physical traits, classifying this as a structural adaptation.
Crown gall is an infectious disease of plants that can cause significant economic losses.
For crown gall disease, explain how the pathogen invades the host and causes disease, and two distinctly different management strategies to prevent the spread of the disease.
The pathogen invade the host and cause disease by first invading the plant through a wound, and inserting plasmid into the host genome. This causes rapid division of host cells, causing galls. Galls disrupt water transport, reducing the ability of plants to resist stressful conditions such as drought.
Management strategies are (any 2 of):
- Avoid damaging the plants, to stop transfer of pathogen from one plant to another.
- Destroy infected plants, to kill bacteria in the environment.
- Apply biosecurity measures at borders, to contain the disease to a certain area.
- Educate people, so people can recognise the disease and act quickly.
How the pathogen invades the host and causes disease
| Descriptor | Marks |
|---|---|
1 mark for each correct point:
| 6 |
Management strategy 1
Marking Bands| Descriptor | Marks |
|---|---|
Identifies a management strategy and explains its purpose (e.g., do not damage plants/clean tools to stop transfer; destroy infected plants to kill/reduce bacteria; apply biosecurity to contain disease; educate people so they can recognise/act) | 2 |
Identifies a management strategy OR its purpose | 1 |
None of the above | 0 |
Management strategy 2
Marking Bands| Descriptor | Marks |
|---|---|
Identifies a management strategy and explains its purpose (e.g., do not damage plants/clean tools to stop transfer; destroy infected plants to kill/reduce bacteria; apply biosecurity to contain disease; educate people so they can recognise/act) | 2 |
Identifies a management strategy OR its purpose | 1 |
None of the above | 0 |
Animals have a variety of behavioural, physiological and structural adaptations to maintain water and salt balance.
Explain what would happen to a desert mammal if it drank saltwater and explain one physiological and one behavioural adaptation that desert mammals use to maintain water-salt balance. State which adaption is physiological and which is behavioural.
Drinking salt water disrupts homeostasis, as body fluids will have too much salt. Cells will lose water to body fluids by osmosis, making them dehydrate.
A physiological adaptation is (insert relevant example). This helps maintain water-salt balance by (any 1 of the following):
- gaining water from food metabolism, where breakdown of fat produces water
- producing hormones, which promote reabsorption of water by the kidneys
A behavioural adaptation is (insert relevant example). This helps maintain water-salt balance by (any 1 of the following):
- being active at night when temperatures are lower, to minimise water loss by evaporation
- burrowing creates humid microclimate to minimise water loss by evaporation
Effects of drinking salt water
| Descriptor | Marks |
|---|---|
1 mark for each correct point (any 4 of):
| 4 |
Explanation of physiological adaptations
Marking Bands| Descriptor | Marks |
|---|---|
States a physiological adaptation AND provides a complete explanation (e.g., gains water from food metabolism by breaking down fat/carbohydrates OR produces hormone/vasopressin/antidiuretic to promote reabsorption of water by kidney) | 3 |
States a physiological adaptation AND provides a partial explanation | 2 |
States a physiological adaptation | 1 |
None of the above | 0 |
Explanation of behavioural adaptations
Marking Bands| Descriptor | Marks |
|---|---|
States a behavioural adaptation AND provides a complete explanation (e.g., nocturnal/active at night when temperatures are lower to minimise water loss by evaporation OR burrows to create humid microclimate/avoid high temperatures to minimise water loss by evaporation) | 3 |
States a behavioural adaptation AND provides a partial explanation | 2 |
States a behavioural adaptation | 1 |
None of the above | 0 |
Xerophytic plants need to maintain water balance while allowing for gas exchange, and have a variety of adaptations to achieve this.
Explain why plants lose water to the environment during gas exchange and three distinctly different ways in which xerophytic plants minimise water loss from gas exchange.
Gas exchange occurs through stomata, which are pores in the leaf. When stomata are open, water is lost from the plant via transpiration/evaporation.
Ways to minimise water loss from gas exchange are (any 3 of):
- Reduced stomata size, such that there's smaller area to lose water through.
- Sunken stomata, which increases humidity around stomatal pore.
- Closing stomata during the day, when temperatures are higher.
- Rolled leaves, which protect stomata from the environment.
Water loss during gas exchange
| Descriptor | Marks |
|---|---|
gas exchange occurs through (open) stomata or plants release oxygen/take in carbon dioxide through (open) stomata | 1 |
stomata are pores in the leaf (that are surrounded by guard cells) | 1 |
water/water vapour is lost from plant when stomata are open | 1 |
via transpiration or evaporation | 1 |
Minimising water loss 1
| Descriptor | Marks |
|---|---|
Identifies a valid strategy to minimise water loss (e.g., fewer stomata/reduced size, sunken stomata/hairs in pit/rolled leaves, stomata open at night/close during day, less stomata on upper surface/more on lower surface) | 1 |
Provides the corresponding explanation for how the identified strategy minimises water loss (e.g., fewer openings/smaller area, increases humidity/creates humid microclimate, open when temperatures are lower, protects stomata from environment/wind/sunlight) | 1 |
Minimising water loss 2
| Descriptor | Marks |
|---|---|
Identifies a valid strategy to minimise water loss (e.g., fewer stomata/reduced size, sunken stomata/hairs in pit/rolled leaves, stomata open at night/close during day, less stomata on upper surface/more on lower surface) | 1 |
Provides the corresponding explanation for how the identified strategy minimises water loss (e.g., fewer openings/smaller area, increases humidity/creates humid microclimate, open when temperatures are lower, protects stomata from environment/wind/sunlight) | 1 |
Minimising water loss 3
| Descriptor | Marks |
|---|---|
Identifies a valid strategy to minimise water loss (e.g., fewer stomata/reduced size, sunken stomata/hairs in pit/rolled leaves, stomata open at night/close during day, less stomata on upper surface/more on lower surface) | 1 |
Provides the corresponding explanation for how the identified strategy minimises water loss (e.g., fewer openings/smaller area, increases humidity/creates humid microclimate, open when temperatures are lower, protects stomata from environment/wind/sunlight) | 1 |
The chance of an epidemic occurring depends on several factors.
Using influenza as an example, explain why urban areas are susceptible to epidemics and how vaccination and three other healthcare provisions can reduce disease transmission.
Influenza is easily spread via direct contact or airborne particles. Urban areas have high population density, which increases disease transmission, as uninfected people are more likely to come into contact with an infected person. Increased travel to urban areas also increases the chance of introducing a new strain with little resistance in the population.
Vaccines give people immunity without catching the disease, which reduces the chances of an individual catching the disease even if they are in contact with an infected individual. The spread of disease will slow if a large proportion of the population are vaccinated.
Other healthcare provisions include education about good hygiene. Healthcare can implement quarantine of infected people, and provide antiviral medication to reduce the severity and duration of symptoms. Monitoring and reporting can result in early detection and early implementation of control measures.
Urban areas
| Descriptor | Marks |
|---|---|
1 mark for each correct point (any 4 of): | 4 |
Vaccinations
| Descriptor | Marks |
|---|---|
States that vaccines give people immunity (without catching the disease) | 1 |
Explains that vaccination reduces the chances of an individual catching the disease (even if they are in contact with an infected individual) | 1 |
Describes that the spread of disease will slow/transmission will be reduced if a large proportion of the population are vaccinated/immune/with herd immunity | 1 |
Other healthcare provisions
| Descriptor | Marks |
|---|---|
1 mark for each correct point (any 3 of):
| 3 |
All animals produce nitrogenous waste, which must be excreted.
Distinguish between how bony fish and land vertebrates excrete nitrogenous waste.
Bony fish mainly excrete ammonia, often via their gills. Ammonia is a by-product of metabolism and requires little to no energy to produce. Although it is toxic, fish can continuously excrete ammonia and do not need to store it because they live surrounded by water in an aquatic environment. However, some marine fish excrete urea due to the need to conserve freshwater.
In contrast, land vertebrates excrete either urea or uric acid, depending on the vertebrate, typically via their kidneys. In these animals, ammonia is converted to urea or uric acid, and this conversion takes energy. Urea and uric acid are less toxic than ammonia, and so can be stored for longer. Furthermore, urea and uric acid need less water to expel, which reduces water needs and is more suitable for land where water is limited. The excretion of uric acid requires less water than urea.
Bony fish
| Descriptor | Marks |
|---|---|
1 mark for each correct point (any 5 of):
| 5 |
Land vertebrates
| Descriptor | Marks |
|---|---|
1 mark for each correct point (any 5 of):
| 5 |
Chytridiomycosis is a major disease of amphibians worldwide, threatening many species with extinction.
Discuss the impact that chytridiomycosis has on the host amphibian.
The disease disrupts skin function because the pathogen infects and damages the outer layer of skin. Breathing is disrupted because amphibians exchange gas, such as CO2 and O2, through their skin.
Osmoregulation is disrupted because ions are transported across the skin. This disrupted ion balance can cause heart failure. The disease also causes neurological effects such as lethargy. These neurological problems can reduce foraging efficiency and make them susceptible to predators, and the disease is often fatal.
Amphibians are particularly susceptible to skin disease because of the importance of their skin in maintaining homeostasis. The effects vary among individuals of a species and between species.
A lot is still unknown about the impact of this emerging disease, and more research is required, such as why susceptibility varies, the pain involved, or the cytology of the disease. Ultimately, it has a huge impact on amphibian biodiversity and populations, and has caused local extinctions.
| Descriptor | Marks |
|---|---|
1 mark for each correct point (any 10 of):
| 10 |