Maintaining the internal environment

Question 1

What are tolerance limits?

Answer 1

All organisms survive most effectively within their tolerance limits, and these are defined by the environmental conditions being within a particular range.

Question 2

State the law of tolerance.

Answer 2

For each abiotic environmental factor, and organism has a range of tolerances within which it can survive.

Question 3

What factors are included in tolerance limits?

Answer 3

Body temperature, water availability, blood glucose level and carbon dioxide concentration.

Question 4

What happens if the environmental conditions fall outside of the organism’s tolerance limits?

Answer 4

It will either not survive, or it must have mechanisms to maintain its own internal environment.

Question 5

For multicellular organisms, what role does extracellular fluid play on maintaining internal composition?

Answer 5

Fluid composition remains constant and enables cells to continue functioning normally. If the tissue fluid is constant, then it is easier for the cells to maintain the conditions needed for their survival.

Question 6

How do multicellular plants maintain their solute and water balance?

Answer 6

Through active transport of solutes in the roots, and by controlling water loss through the leaves by closing the pores of their stomata.

Question 7

When does the organism respond to changes in its environment?

Answer 7

Organisms are selective in their response to such changes, only responding to those that are possibly going to affect it.

Question 8

What factors affect the growth of plants?

Answer 8

• Mineral composition of soil
• Light availability
• Carbon dioxide levels
• Temperature
• Wind
• PH of the environment

Question 9

State Leibig’s law.

Answer 9

The environmental factor that is in least supply will limit productivity.

Question 10

What is eutrophication?

Answer 10

The result of an excess of nutrients (phosphorus and nitrogen) into waters, and higher concentrations of these nutrients in water cause increase growth of algae and green plants.

Question 11

What is the effect of eutrophication on the environment?

Answer 11

As more algae and plants grow, other organisms die due to the blocking of sunlight. This dead organic matter becomes food for bacteria that decompose it. With more food available, the bacteria increase in number and use up the dissolved oxygen in the water. When the dissolved oxygen content decreases, many fish and aquatic insects cannot survive which results in a ‘dead area’.

Question 12

Define homeostasis.

Answer 12

Organisms detect and respond to changes in the internal and external environment. Homeostasis is the maintenance of the ‘steady state’ in response to changes.

Question 13

What are the types of mechanisms to achieve homeostasis?

Answer 13

• Structural: physical features (e.g., body covering)
• Physiological: internal processes that detect and respond to changing conditions (e.g., metabolism)
• Behavioural: behaviours that aid in survival (e.g., hibernation)

Question 14

List the order of the stimulus response model.

Answer 14

Stimulus > receptor > transmission > effector > response

Question 15

In regard to the stimulus response model, define stimulus.

Answer 15

Refers to the variation in the internal or external environment (usually a physical or chemical change) that is able to be detected by the organism, leading to a response controlled by the nervous system.

Question 16

In regard to the stimulus response model, define receptors.

Answer 16

Cells or tissues that can detect a change and generate nerve impulses or release specific hormones.

Question 17

In regard to the stimulus response model, define transmission.

Answer 17

refers to the relay of information by nerves and/or hormones.

Question 18

In regard to the stimulus response model, define effectors.

Answer 18

Glands or muscles that elicit a response after receiving information.

Question 19

In regard to the stimulus response model, define response.

Answer 19

An action which occurs due to the initial stimulus.

Question 20

In regard to the stimulus response model, define feedback.

Answer 20

The impact of the response on the initial stimulus (can be positive or negative).

Question 21

What is the role of a sensory receptor?

Answer 21

They detect stimuli such as light, chemicals, sound, temperature and touch. Humans have five main types: hearing, touch, sight, smell and taste.

Question 22

What are the locations for sensory receptors?

Answer 22

• Seeing, tasting, smelling and hearing are located in specialised sense organs in the head.
• Somatic sensation (such as temperature and touch) are distributed over the skin and muscles.

Question 23

How do sensory receptors detect?

Answer 23

They respond to the intensity, duration and location of the stimulus. Once the receptiors have been stimulated, they send a nerve impulse to the CNS; there the signal is processed and interpreted. The CNS sends a nerve impulse along motor neurons (nerve cells) which signal the effectors, such as muscle cells or glands, to respond

Question 24

What is negative feedback?

Answer 24

When considering a particular variable in the body, if any change triggers a response that counteracts the initial fluctuation, then the process is referred to as negative feedback.

Question 25

What is the role of negative feedback?

Answer 25

Such mechanisms prevent small changes from becoming too large.

Question 26

What is positive feedback?

Answer 26

In the case that a change in some variable triggers a response that amplifies rather than reverses the initial fluctuation, it is called positive feedback.

Question 27

What is the main difference between positive and negative feedback?

Answer 27

Positive feedback mechanisms enhance the original stimulus, while negative feedback mechanisms inhibit it.

Question 28

As the stimulus increases...

Answer 28

...the response increases, and this then inhibits the stimulus. As a result, the stimulus fluctuates about a pre-set level.

Question 29

In human beings, what does homeostasis depend on?

Answer 29

The functioning of the nervous and endocrine systems.