Biology

HideShow resource information

Our Senses

Sound
-Ears
-Detects soundwaves

Smell
-Nose
-Detects scents
-Has chemical receptors

Taste
-Tongue
-Has chemical receptors

Touch
-Skin
-Detects pressure, pain, temperature

Sight
-Eyes
-They detect light

Receptors- special cells that detect stimuli
Stimuli- anything that triggers a response

1 of 9

Hormones

Hormones are chemicals (protein mmolecules) which travel around the body in the blood-stream. They are made by glands and travel to target organs where they have their effects. Hormones are slow acting and longer lasting than those of the nervous system

FSH (Follicle- Stimulating Hormone)
-Made in the Pituitary Gland
-Travels in the bloodstream to the ovaries
-Starts to mature an egg
-Tells the ovaries to release the oestrogen
-If FSH isn't switched off it can cause multiple pregnacys

Oestrogen
-Made by the Ovaries
-Continues to mature the egg
-Thickens the womb lining
-Switches off FSH production by the pituitary gland

LH (Luteinizing Hormone)
-Made by the pituitary gland
-Causes ovulation on day 14 (approx)

2 of 9

Menstrual Cycle

The menstrual cycle is controlled by hormones. On day 1 of the menstrual cycle, the period starts but the pituitary gland also starts to release FSH. FSH travels in the blood-stream to the ovary and starts an egg to mature, it also triggers the ovary to produce Oestrogen. Oestrogen switches off any further FSH production so only 1 egg (ovum) matures and the womb lining is thickened. Oestrogen now triggers the release of LH on day 14, from the pituitary gland. LH causes ovulation the release of the egg from the ovary. Women are most fertile at this time of the 24th day of the menstrual cycle. If the egg is not fertilised all of these hormones drop in level and by day 28 they have such a low level the womb lining can no longer be maintained so womens periods start.

3 of 9

The contraceptive pill and fertility drugs

The contraceptive pill contains Oestrogen which switches off the production of FSH. Without FSH no eggs mature in the ovaries and no eggs ovulate therefore a woman cannot become pregnant

Pros:
+ allows coitus without pregnancy
+ allows choice of family size
+ economic benefits
+ choice of when to have a child
+ control population size
+ 99% effective if taken carefully

Cons:
- side effects on health
- not 100% effective
- expensive to produce
- leads to 'promiscuous' behaviour

4 of 9

The contraceptive pill and fertility drugs

The fertility drug contains FSH or LH. It encourages the ovaries to mature eggs or it encourages the ovaries to mature eggs or it encourages ovulation (LH).

Pros:
+ allows couples to have a child of their own

Cons
- expensive
- risks of multiple births (too many eggs mature)
- side effects
- ethical issues

5 of 9

Homeostasis

Homeostasis is maintaining a constant internal enviroments. We need to keep our internal environment the same at all times to ensure all our reactions take place at an optimum rate.

The organs of Homeostasis are:
- The kidneys
- The Pancreas
- The skin
- The liver
- The lungs

Kidneys
The kidneys are made of millions of small tubules.
These tubules filter the blood, removing excess salt and water and urea. The kidneys make urine.

Liver
The liver has many jobs it makes bile which helps with fat digestion. It is also impportant in detoxifying the blood by breaking down harmful toxins and drugs.

6 of 9

Homeostasis

Lungs
Carrys out gas exchange, they remove toxic and acidic CO2 from the body.

Pancreas
Makes insulin
Controls blood sugar level
The brain cannot toleratehigh or low blood sugar levels

Skin
Controls temperature
Regulates our temperature at 37oC. If we are too hot it sweats and more blood is diverted to it.
If we are cold we do not sweat and blood is diverted away from the skin, we get pale.

Homeostasis is vital to ensure our enzymes work effectively. Enzymes do not function if pH, temperature of the body fluctuates

7 of 9

Phototropism

The shoots of a plant are positively phototropic. This means stems grow towards the light. Phototropism is controlled by hormones called Auxins.

1. Sunshines on a plant from one side.
2. Auxin gathers on the shady side.
3. Auxin makes the cells on the shady side grow more and cells elongate. This causes the plant to bend towards the light.

8 of 9

Phototropism, Hydrotropism and Geotropism

Auxin gathers on                                                                            The shoot bends towards
the shady side so                                                                            the sunlight for photo-
the cellshere grow                                                                           synthesis
and elongate faster                                                                         Positive Phototropism

Auxin gathers on
the underside of the
roots. This slows cell
growth and elongation
so the roots grow towards
the water and gravity:
Positive Hydrotropism
Positive Geotropism

9 of 9

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »