B1 Plant hormones

Remember the notes on hormones in the human body? Hormones travel in the blood as chemical messengers to tell parts of the body what to do. Example, the pancreas releases the hormone insulin to signal the liver to remove excess glucose from the bloodstream.

Well, plants have hormones as well - honest!

These hormones which are also called plant growth substances allow the plant to respond to stimuli.

Now, responding to a stimulus by either growing towards it or away from it is called a tropism. You have to know about 2 types of tropisms.

1. Phototropism where the plant responds to light.
2. Geotropism where the plant responds to gravity.

A tropism where the plant moves away from the stimulus is called a negative tropism.

A tropism where the plant moves towards the stimulus is called a positive tropism.

So, different parts of the plant respond differently to different stimuli.

The plant stem bends towards the light so this is positive phototropism. 

The plant stem grows away from gravity so this is negative geotropism.

Now the plants roots do the opposite of this.

The roots grow downwards towards the direction of gravity so this is positive geotropism.

The roots grow away from light so this is negative phototropism.

So far so good, I hope. So the shoots grow towards the light and the roots grow downwards towards the centre of gravity - but how?

Well, strange as it may seem, plants just like us make hormones - honest!

Now, we make hormones from our glands - plants make hormones which are also called plant growth substances, from cells in the tips of the shoots or the roots. 

There are 3 plant hormones that you must learn.

Positive phototropism in the shoots is caused by plant hormones called auxins.

Positive gravitropism in the roots is also caused by plant hormones called auxins.

There are also plant hormones called gibberellins. 

These are produced  when a seed starts to germinate and grow shoots and roots. 

These hormones cause the starch stored in the seed to be broken down into glucose (sugar) which is used in respiration. Respiration makes energy for the seed to grow into a plant.

Now for the fine detail. 

How do the auxins (plant hormones) actually cause the shoots and roots to bend?

1. In phototropism the auxins are made in the tip of the shoot where they cause the cells to get longer - they elongate. If the light on the plant was directly above, then all the cells in the shoot tip would elongate so the plant would go straight up. If the plant had light from only one side, say it was a plant growing on a window sill. Then the auxins move to the shaded part of the shoot tip. The cells elongate and get longer which makes it bend towards the light.
2. Now there are also auxins found in the root tips and just to be awkward they do the opposite of the auxins in the shoots! In roots, auxins cause the cells to stop elongating - it is this that causes positive gravitropism or geotropism. Basically the auxins in a root are pulled downwards by gravity and inhibits or stops cell elongation. The cells on the other side still get longer so the root bends and grows downwards.

So,

In a shoot, the auxins make the cells elongate.

In a root, the auxins stop the cells elongating.

Even more plant hormones.

There are other plant hormones called gibberellins - there would be eh?!
When a seed germinates a root and a shot has to grow. The seed needs energy to grow. As it isn't photosynthesising yet (because there is no light for the shoot yet) the seed does something else. It releases plant hormones called gibberellins which cause the starch in the seed to be broken down into sugars for use in respiration to make energy.

B1 Ethics and transplants

B1 The effects of alcohol

Wouldn't it be nice if drinking alcohol always made you happy and there were no side effects?!

Well unfortunately it isn't like that - alcohol is a type of drug called a depressant. It is quickly absorbed into the bloodstream where it goes to the brain and nervous system. This affects the reaction times so that it takes longer to respond.

Drinking alcohol also lowers your inhibitions so that you are more likely to to do things that you wouldn't normally do - including taking greater and sometimes stupid risks.

Short term effects:

1. blurred vision.
2. lowering of inhibitions - as said previously.
3. slowing of reactions  - as said previously.

Long term effects:

1. liver cirrhosis - this where the liver cells are damaged.
2. brain damage.

Alcohol can also be addictive. People who become addicted to alcohol and depend on it are called alcoholics.

B1 Damage caused by smoking

Smoking is bad for you - OK

But  

- as you will be sitting a science GCSE you have to be scientific so give specific detailed answers!

Tobacco smoke contains many chemicals that can damage living tissue.

Tar in the smoke is a carcinogen - this means that it can cause cancer!

Another chemical that causes you damage is the gas Carbon monoxide.

This poisonous gas joins with the haemoglobin in red blood cells. If the red blood cells are carrying Carbon monoxide then they are not carrying Oxygen! We need Oxygen for respiration.

A lack of Oxygen to active muscles can cause pain.

Carbon monoxide also makes blood vessels narrower. So, these blood vessels can therefore carry even less oxygen so the cells that the blood vessels reach may even die. If the heart doesn't get enough Oxygen then you might get a heart attack and even die.

Carbon dioxide and other gases in the smoke can also cause emphysema and chronic bronchitis.

Nicotine is the big problem - it is addictive.

It is the nicotine in tobacco smoke that makes it difficult to give up - even if you know the tar is killing you.

B1 Effects of drugs

What is a drug?

Learn this - 

A drug is a chemical substance that affects the central nervous system causing changes in psychological behaviour and possible addiction.

There are many different types of drugs so to make things easier they are classified into different groups.

1) Painkillers -  We feel pain when electrical impulses from a damaged part of the body are sent via sensory neurones to the brain. Narcotic painkillers, such as morphine, block some of these nerve impulses, so we feel less pain. These drugs can also make us sleepy.


2) Hallucinogens - These are drugs that change the way the brain works. These distort sense perception and so change how we respond to what we see, hear and feel. Hallucinogenic drugs like LSD can distort our senses of colour, time and space.

3) Stimulants - These drugs increase the speed of neurotransmission of nerve impulses across synapses. This speeds up reaction times so we use less time - we are quicker. Caffeine is a stimulant.

4) Depressants - These drugs slow down the activity of neurones in the brain and can help us relax. Alcohol is a depressant.

Some drugs are legal (like caffeine in fizzy drinks) and others are illegal like heroin. Some drugs are legal at certain ages to buy like alcohol whilst some illegal drugs like heroin are used in hospitals, but under very controlled conditions. Some drugs are recreational where they are used by people to feel in a certain way like alcohol. Other drugs are medicines to help against injuries or illnesses.

Most drugs are addictive which means that people become dependent on it and feel that they can't function properly without it.

B1 Uses of plant hormones

Plant hormones can be used by us for many things rather than just for the plant to bend the shoot towards the light or bend the root downwards because of gravity.

1) Selective weedkillers.
2) Rooting powder.
3) Seedless fruit.
4) Fruit ripening.

Selective weedkillers are made from artificial auxins. These only work on broad-leaved plants like daisies and dandelions - weeds! They make the plants grow out of control and die. So, you could use this weedkiller on your lawn or a farmer spraying his fields to kill weeds and so leave more room for his crops.

Rooting powders also use synthetic or artificial auxins. Here, plant cuttings are dipped in the rooting powder which causes the bits of plants to grow roots faster.

Seedless fruit can be made when the flowers are sprayed with plant hormones that cause the fruits to develop but not the seeds. Some varieties of grapes have naturally seedless fruit but they are too small. These can be sprayed with gibberellins to make them bigger.

Fruit ripening can be controlled by spraying with plant hormones. This could speed up the fruit ripening or even stop them falling off the tree and getting damaged. The fruit would also get bigger.