5.1 glass houses

• glasshouses/greenhouses have frameworks made of glass which lets light penetrate through
• the frame is made out of polythene which also lets light penetrate

how greenhouses work:
• solar radiation from the sun
• light goes through glass
• light is absorbed by surfaces inside greenhouse e.g. soil, plants
•  these surfaces will re-emit this energy as heat
• the heat warms the air raising its average KE, raising the overall temperature
• the warm air is trapped

warm air glasshouse = higher crop yield

this is because:
- high temp = optimum temperature for enzyme reactions (photosynthesis)
- temperature is constant throughout the year
- prevention of loss of water vapour - crops do not dry out, because they have a constant supply of water (vapour)
- avoid frost damage (especially seedlings)
- glasshouses are warmed by the burning of fossil fuels which leads to an increase in the CO2 levels inside the glasshouse (increased substrate for photosynthesis, increasing growth). inefficient burning of fossil fuels results in ethane being produced which is a gas that stimulates fruit ripening

2.89

understand the sources, roles and effects of the following hormones: ADH, adrenaline, insulin, testosterone, progesterone and oestrogen.

2.88

describe the role of the skin in temperature regulation, with reference to sweating vasoconstriction and vasodilation


our skin has many different sensors. our fingers tips have the greatest amount of sensors
they protect skin,stops too much water loss, help you keep your body temperature constant, stop germs getting in and ket you feel pain, temperature.


vasoconstriction: happens when cold, the blood vessels become narrower and the flow of blood is constricted, resulting in retained body heat. your skin turns paler as less blood is reaching the surface, reducing the radiation of heat.


vasodilation: happens when hot, blood vessels widen, resulting in increased blood flow and lower blood pressure

2.87

understand the function of the eye in focusing near and distant objects, and in responding to changes in light intensity

bending the light rays is done by the curved cornea and lens

cilary muscles control the shape of the lens

focusing on close objects

contraction of cilary muscles, which slackens the suspensory ligament and the lens becomes rounder. this image is then focused on the retina

focusing on distant objects

cilary muscles relax, which tightens the suspensory ligament and the lens becomes flatter. this image is then focused on the retina

2.86

describe the structure and function of the eye as a receptor


eyes are located in two sockets in the skull and moved by 3 pairs of muscles
the light enters the eyes through the cornea, which is transparent and at the front of the eye
then the light goes through the pupil
the cornea has a delicate and transparent layer in front of it called the conjuctiva
this kept moist by tear glands which 'wash' your eyes when you blink
























process of seeing things
after the light enetering through the cornea, it passes through the lens and hits the retina 
the retina contains cells called rods and cones which are sensitive to light.
as light hits and stimulates them, they send signals down the optic nerve to the brain.
your brain then interprets the impulses as images


the image is actually inverted but the brain has adapted to turning it the right way around
rod cells = react to dim light
cone cells = react to colour and detail

2.85

describe the structure and functioning of a simple reflex arc illustrated by the withdrawalof a finger from a hot object


reflexes happen very fast so you dont harm yourself
reflex arc = the pathway to an impulse along the neurons


stimulus: hot object


receptor: skin


coordinator: brain (hypothalamus) 


effector: muscles in hand


response: hand pulls away from/drops hot object

2.84

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

neurons: 

-nerves have cell membranes, cytoplasm, and nucleus but are a different shape to other cells

-part of the cell is stretched to form the axon.

-the axon can be many meters long

how nerve messages travel

- the messages that nerves carry are sent by nerve impulses, which are electrical

- as a result of this the message travels very fast through the axon

some axons (such as mammals') have fatty sheaths around them that make the nerve impulses travel faster since the fat insulates the axon and makes the impulse travel faster