2.77 Understand that organisms are able to respond to changes in their environment.
This is called Sensitivity, and is one of the Mrs C. Gren Life Processes.
To be able to detect change in their environment living things must have receptors and effectors to be able to carry out a response.
To be able to detect change in their environment living things must have receptors and effectors to be able to carry out a response.
2.78 Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis.
Homeostasis: The maintenance of constant internal environment.
This includes:
This includes:
- Osmoregulation: The control of water levels in the body
- Thermoregulation: The control of temperature in the body (as ideal body temperature is 37ºC)
- When you are hot you sweat - So the heat is absorbed from your skin -
- When you are cold you body hairs stick out - To trap air as a layer of insulation.
2.79 Understand that a coordinated response requires a stimulus, a receptor and an effector.
A response: is a behaviour which is caused by stimulus
For a response to be carried out, it required to have:
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Flowering Plants
2.80 Understand that plants respond to stimuli.
Plants respond to stimuli. They will react to changes in the environment, like temperature and light.
Usually the response is carried out by plant hormones. A common example for iGCSE is Auxin. Auxin stimulates plant growth, stimuli for this are often light (photo-tropism), or gravity (geo-tropism). (Water, hydro-tropism is also a stimuli but you do not need to know this for iGCSE). |
2.81 Describe the geotropic responses of roots and stems.
2.82 Describe positive phototropism of stems.
Phototropism: The growth of a plant in response to the direction of light.
Positive phototropism: The growth towards light. (This happens in the stems). Negative phototropism: The growth away from light. (This happens in the roots). Where there is a lot of light there are few auxins, compared to when there is little light there will be many auxins. If one of of a stem receives a lot of light and the other side does not is causes the stem to bend towards the light. This happens due to the imbalance of auxins. This is called cell elongation. |
Humans
2.83 Describe how responses can be controlled by nervous or by hormonal communication and understand the differences between the two systems.
The nervous system and the endocrine system (hormonal) both coordinate responses within the body.
This table shows the differences:
This table shows the differences:
2.84 Understand that the central nervous system consists of the brain and spinal cord and is linked to sense organs by nerves.
An human's response to a stimulus is coordinated by its central nervous system (CNS).
The CNS consists of the brain and the spinal cord. These are connected to the sensory organs (receptors) by nerves.
The CNS consists of the brain and the spinal cord. These are connected to the sensory organs (receptors) by nerves.
2.85 Understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses.
Receptors send a electrical impulse through nerves towards the CNS, when stimulate by a stimulus.
This message goes via the Sensory Neuron. A Relay Neuron carries the impulse through the CNS. When a response decided it is sent back out in electrical impulses via the Motor Neuron to the effector. These impulses are very fast, as is the reaction time.
This message goes via the Sensory Neuron. A Relay Neuron carries the impulse through the CNS. When a response decided it is sent back out in electrical impulses via the Motor Neuron to the effector. These impulses are very fast, as is the reaction time.
2.86 Describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object.
A reflex is an automatic reaction.
A reflex arch is the path of the reaction,
An example is: removing your hand from extreme heat.
A reflex arch is the path of the reaction,
An example is: removing your hand from extreme heat.
- It starts at a sense organ (e.g a finger)
- Receptors pick up stimuli (e.g heat)
- Sensory neurones carry an electrical impulse to the CNS via a Sensory Neuron
- A Relay Neuron carries the impulse through the CNS where a response is decided
- The new impulse is sent through a Motor Neurone
- This makes an effector carry out a response (e.g muscle contracts to bring finger away from heat).
2.87 Describe the structure and function of the eye as a receptor.
The eye is a receptor of light, it has light receptor cells in its retina. These cells turn stimuli into electrical impulses.
2.90 Understand the sources, roles and effects of the following hormones: ADH, adrenaline, insulin, testosterone, progesterone and oestrogen.
ADH
Lack of water is detected by the hypothalamus in the brain, it causes the pituitary gland to produce Anti-diuretic hormone, or ADH. This makes the kidneys to reabsorb more water- so less is lost from the body.
Adrenaline
Produced in the adrenal glands in stressful situations. Heart rate quickens to increase the flow of blood to muscles- this means that they can respire more (as there is more oxygen available) to provide energy if you need to 'fight or flee'.
Insulin
Produced in the pancreas when there is too much glucose in the blood. It stimulates cells to convert the glucose into glycogen which is a from that can be stored. This means that you always have the right amount of glucose in your blood.
Testosterone
Produced in ovaries in girls and testicles in boys. Plays a key role in puberty, developing sex organs and inspiring hair growth.
Progesterone
Produced in the ovaries it maintains the lining ready for pregnancy, and continues to do so if the egg is fertilised.
Oestrogen
Produced in the ovaries, it is controls other hormones to regulate the menstrual cycle. It stops the production of FSH and starts the production of LH.
Lack of water is detected by the hypothalamus in the brain, it causes the pituitary gland to produce Anti-diuretic hormone, or ADH. This makes the kidneys to reabsorb more water- so less is lost from the body.
Adrenaline
Produced in the adrenal glands in stressful situations. Heart rate quickens to increase the flow of blood to muscles- this means that they can respire more (as there is more oxygen available) to provide energy if you need to 'fight or flee'.
Insulin
Produced in the pancreas when there is too much glucose in the blood. It stimulates cells to convert the glucose into glycogen which is a from that can be stored. This means that you always have the right amount of glucose in your blood.
Testosterone
Produced in ovaries in girls and testicles in boys. Plays a key role in puberty, developing sex organs and inspiring hair growth.
Progesterone
Produced in the ovaries it maintains the lining ready for pregnancy, and continues to do so if the egg is fertilised.
Oestrogen
Produced in the ovaries, it is controls other hormones to regulate the menstrual cycle. It stops the production of FSH and starts the production of LH.