Homeostasis

What is homeostasis?

Maintenance of a constant internal environment despite fluctuations in the external environment

Why is homeostasis important?

Homeostasis ensures that the fluid environment (tissue fluid) of the cells:

• maintains optimum concentration of nutrients, ions, gases and water

• maintains optimum temperature

• metabolic wastes are removed

• maintains optimum pH

What is the effect of high and low concentrations of light on metabolic activities?

Light is used for photosynthesis

High: increases photosynthesis, higher productivity

Low: limits photosynthesis, decreased productivity

What is the effect of high and low concentrations of carbon dioxide on metabolic activities?

Carbon dioxide is used for photosynthesis
High: increases photosynthesis, higher productivity
Low: limits photosynthesis, decreased productivity

What is the effect of high and low concentrations of water on metabolic activities?

Water is used for photosynthesis, turgidity, guards cells open, mineral transport

High: turgid cells, stomates open, xylem flow high, increase photosynthesis

Low: flaccid cells, stomata close, xylem flow reduced, decreased photosynthesis

What is the effect of high and low concentrations of temperature on metabolic activities?

Temperature effects rates of chemical reactions, including photosynthesis

High: may denature enzymes disrupting metabolism

Low: slows metabolism including photosynthesis/respiration

What is the effect of high and low concentrations of nutrients on metabolic activities?

Nutrients are used for coenzymes and synthesis of organic molecules

High: externally causes water loss from plants

Low: disrupting metabolism, low osmotic potential, growth reduced

What is the effect of high and low concentrations of soil pH on metabolic activities?

High: effect enzymes and disrupt metabolism

Low: effect enzymes

What is the effect of high and low concentrations of oxygen on metabolic activities?

Oxygen is used for respiration

High: high rates of respiration

Low: low respiration rate and low cell activity

What is a feedback system?

A feedback system is how the body or cells respond to a stimulus (a change in the environment) to maintain a constant internal state.

What are the components of the stimulus-response model?

• stimulus

• receptor

• modulator/coordinating centre

• effector

• response

• feedback.

How does the stimulus work in a feedback system?

• the initial change in the internal or external environment that disrupts homeostasis.

• It is detected by receptors, which then initiate a response to counteract the change and restore balance

How does the receptor work in a feedback system?

• detects the change in the external or internal environment

• sends information to the modulator

How does the modulator/coordinating centre work in a feedback system?

• Modulator registers the change from the receptor and initiates a response.

• it sends signals to the effectors

How does the effector work in a feedback system?

• Effector is a structure or organ which carries out the response directed by the modulator

• it counteracts the original stimulus and restores homeostasis

How does the response work in a feedback system?

Response is the action taken in response to the stimulus. Most animals use nerves or hormones in this process.

How does the feedback work in a feedback system?

• Feedback is how the response changes the original stimulus.

• If it reduces the stimulus, it is called negative feedback and is used to achieve homeostasis.

• If it increases the stimulus, it is called positive feedback.

What is the negative feedback system?

• The negative feedback system is the response reduces/opposes the stimulus.

• If the original change is an increase in body temperature, negative feedback will be a decrease in body temperature.

• Negative feedback brings change back to optimum level.