5.1.1 Communication And Homeostasis

Question 1

Why do multicellular organisms need communication systems?

Answer 1

In order to survive organisms need to be able to respond to changes in their external environment e.g. by avoiding harmful situations such as places too hot or cold. Also respond to internal environment to make sure conditions are always optimal for their metabolism

Question 2

What is a stimulus?

Answer 2

Any change in the internal or external environment e.g. change in temp, light intensity or pressure

Question 3

Give 2 examples of communication systems?

Answer 3

Nervous and Hormonal systems

Question 4

What is a receptor and give two examples?

Answer 4

Detect stimuli and are specific to one particular stimulus
Mechanoreceptors - pressure
Photoreceptors - light

Question 5

What is an effector and give an example?

Answer 5

Cells that bring about a response to a stimulus, to produce an effect
They are muscles and glands
E.g. the pancreas

Question 6

What is cell signalling and give 2 systems in which is occurs?

Answer 6

Receptors interact with effectors and effectors interact with other cells to induce a response. This can occur between adjacent (nearby) cells or between distant cells.
E.g. cells in NS communicate by secreting chemicals called neurotransmitters, which send signals to adjacent cells such as other nerve cells or muscle cells
E.g. in the hormonal system the adjacent cells release chemicals called hormones, which travel in the blood + acts as signals to distant cells, then cell surface receptors allow cells to recognise the chemicals involved in cell signalling

Question 7

FRQ- Why is it important that organisms respond to stimuli?

Answer 7

To increase their chances of survival - they respond to their environment

Question 8

FRQ - Give one reason why communication systems are needed in multicellular organisms?

Answer 8

To ensure that the activity of diff. organs are co ordinated to keep the organism working effectively

Question 9

FRQ - What is cell signalling?

Answer 9

The way in which cells communicate with other cells

Question 10

Define Homeostasis

Answer 10

The maintenance of a constant internal environment

Question 11

Impact of TEMP

Answer 11

As temp increases so does rate of metabolic reac as
more heat means more kinetic energy so molecules move faster
Substrate molecules are more likely to collide with enzyme’s active sites
The energy of these collisions also increases which means collisions are more likely to result in a reac
IF TEMP TOO HIGH:
Reac slows down as temp is way above optimum temp for enzymes - thus tertiary structure impacted (hydrogen bonds are broken), thus as 3D shape changes so does enzyme’s active site thus is no longer complimentary with substrate (DENATURED) an so cannot function as a catalyst
IF TEMP TOO LOW:
Enzyme activity is low thus metabolic rate of reac is also slower

Question 12

Define Negative feedback

Answer 12

When their is a change in the environment the body works to counteract that change to bring the level back to normal

Question 13

Name the steps of a negative feedback loop/mechanism? (5 stages)

Answer 13

1. At normal level
2. Level changes from normal
3. Receptors detect change
4. Communication via nervous or hormonal system
5. Effectors respond and bring it back

Question 14

What happens if the change is too large + give an example?

Answer 14

Negative feedback only occurs within a specific range and if the change goes beyond that then the effectors may not not be able to counteract the change
E.g. a huge drop in body temperature caused by prolonged exposure to cold weather may be too large to counteract

Question 15

Define Positive Feedback

Answer 15

When a change in the environment causes the effectors to amplify the change (further increase the level away from normal level)

Question 16

Name the steps of a Positive Feedback loop (5 stages) ?

Answer 16

1. Normal level
2. Normal level changes
3. Receptors detect change
4. Communication via nervous or hormonal system
5. Effectors respond to increase change further from normal level

Question 17

Is positive feedback involved in homeostasis and what is its function?

Answer 17

No as it does not aim to keep the body’s internal environment constant but is useful to rapidly activate processes in body.

Question 18

Give an example of positive feedback?

Answer 18

Formation of blood clot after an injury, platelets become activated + release a chemical that triggers more platelets to be activated therefore platelets can form a blood clot very quickly at injury site.
The process ends with negative feedback when body detects that blood clot has formed.

Question 19

Define Ectotherm and give an example

Answer 19

They cannot control their body temp internally, they control their temperature by changing their behaviour.
E.g. a lizard is an ectoderm where when it’s internal temp drops, a lizard will move to a warmer area + bask in sun, when its internal temp is too high it will move to cooler area i.e burrowing beneath the sand
This means the internal temp of ectotherm depends on the external temperature (surroundings/environment)

Question 20

How does being an ectotherm impact metabolic rate?

Answer 20

They have a variable metabolic rate as the cannot keep internal temp constant, thus they generate very little heat themselves
This means activity of ectotherm relies on external temp too - they are more active at higher temp + less active at lower temps

Question 21

Define Endothermic and give an example

Answer 21

They control their body temperatures internally by homeostasis, as well as altering their behaviour
E.g. an elephant is an endotherm where its temp is mainly controlled internally by homeostasis, but it may also change its behaviour i.e. may wallow its mud or flap its ears to help cool down

Question 22

How does being an endotherm impact metabolic activity?

Answer 22

Compared to ectotherms, the internal temp of endotherm is less affected by external temp (within certain limits) thus endotherms have constantly high metabolic rtes as they can keep internal temp constant - they generate a lot of heat from Metabolic reac
Therefore, endotherms activity evens are largely independent of external temperature - they can be active at any temperature (within certain limits)