B1 Tropic responses

A tropism is where a living organism grows or moves towards a stimulus.

It usually happens in plants but can also happen in animals.

In plants the stimuli could be light or gravity.

Roots respond to gravity by growing downwards.

Leaves and the stem respond to light by growing towards it.

Easy and obvious eh?!

B1 Diabetes

Diabetes is an important topic that many pupils make a mess of because they haven't really learned about what does what to what and when - clear as mud eh?!

Remember, diabetes is where people have a disease where they cannot control their blood sugar levels very well. So it's an example of where homeostasis is not working. Homeostasis is where we control our internal environment.

Is it important that you control your sugar levels? Yes it is!!!

Low blood sugar levels can cause unconsciousness.

High blood sugar levels can damage organs such as your eyes.

There are 2 different types of diabetes and you must learn the differences.

Type 1 diabetes

This is where the pancreas does not make insulin. This means that when they eat something and their sugar levels rise then there is nothing to tell the liver to remove excess glucose. So, people with Type 1 diabetes usually inject insulin every day. The insulin has to be injected into the fat layer just beneath the skin - this is called the subcutaneous fat layer. Fat easily absorbs the insulin where it then spreads into the blood capillaries and is carried around the body to the liver in the blood stream.

Type 2 diabetes

Type 2 diabetes happens when the cells in a persons body respond less well to insulin - the cells start to become 'resistant' to insulin even though the pancreas is still making the hormone. Doctors have worked out the many reasons that can cause type 2 diabetes like being obese, lack of exercise, getting older and having a high fat diet.

Type 2 diabetes can often be controlled by changing:

1) their diet - eating less fat and glucose.

2) increasing their exercise to use up excess glucose through respiration.

B1 Hormones

What are hormones?

Hormones are basically chemicals that are made and released by glands called endocrine glands. These messages go into the bloodstream where they cause certain parts of the body to do something. Different messages for different parts of the body.

So where are these endocrine glands then?





There are lots of them and they send chemical messages to specific target organs.

1. Pituitary gland releases anti-diuretic hormone which causes the kidneys to produce more concentrated urine. This is part of homeostasis which helps keep our water levels constant.
2. Adrenal gland makes the hormone adrenaline which speeds up the heartbeat.
3. The pancreas releases the hormone glucagon which raises blood glucose levels and also the hormone insulin which lowers blood glucose levels. This is a big topic which you will have to learn especially linked to diabetes Types 1 and 2.
4. The male testes release the hormone testosterone which causes the development of the male reproductive organs during puberty.
5. The female ovaries make the hormone oestrogen which causes the development of the female reproductive organs during puberty.

Now, let's get back to the the control of blood sugar levels.

You eat, in fact you may usually eat your lunch at break-time. 

Carbohydrates in your food are mainly digested into a type of sugar called glucose. So, eating carbohydrates (like bread, flour, cakes. potatoes etc) increase the glucose levels whereas exercise, in fact respiration uses up glucose so the blood sugar levels drop.

Note, energy stored in food is released in respiration. Respiration is not breathing!

So, all the time your glucose levels are going up and down depending on what you are doing. Homeostasis is keeping the internal environment stable - in this case it is to do with keeping the blood sugar levels the same.

Now, this topic is about hormones,
so it's basically a gland sending a chemical message to tell something else what to do.

It's the pancreas that makes the hormones

.

The 2 hormones are called insulin and glucagon.

The target organ is the liver.

The pancreas then is telling the liver what to do by sending it 2 messages.

1. Insulin tells the liver that there is too much glucose in the blood so it has to remove some. The liver takes the glucose out and stores it as glycogen.
2. Glucagon tells the liver that there is not enough glucose in the blood (the glucose has gon!) so the liver breaks down the glycogen stored earlier back into glucose. 

B1 Responding to stimuli

When the brain gets impulses from the receptor cells it co-ordinates a response. What this means is that the brain sends impulses to effectors and these do something. Effectors could be muscles or glands. Like your brain could send an impulse to your sweat glands to make sweat to cool you down. So the effectors do something - they have an effect.

Right now, lets get the basics sorted.

The neurones that receive impulses from receptor cells are called sensory neurones.

That makes sense doesn't it - the sensory neurone senses things because it is receiving information.

The neuron in the diagram above has lots of dendrites - these are to receive the information. This information is passed along the neurone as an impulse. The impulse travels along the neurone along the axon. Remember, the myelin sheath is a fatty layer that insulates the axon so the impulse moves faster.

It does not protect the axon!

The neurones that take impulses to effectors are called motor neurones.

Effectors are the things that make an effect - they could be the muscles.

Motor neurones do not have a dendron, the dendrites are on the cell body.

Relay neurones are short neurones that join up the motor neurones and the sensory neurones. These neurones are found in the spinal cord and the brain.

Now, so you've got all these neurones joining with each other. Well, there is a bit of a problem. Where the neurones connect with each other there is a small gap called a synapse. Impuses are transmitted across the gaps in synapses by chemicals called neurotransmitters. Stimulants like caffeine speed up the neurotransmission of nerve impuses across the synapses.


The synapse actually slows down the impulse but they are useful because as the chemicals are only released from the axon endings the impulse can only go in one direction. Botox injections stop impulses from the motor neurones reaching the muscle cells. This stops the muscle cells working so the skin doesn't wrinkle.

The reflex arc - learn it!
The reflex arc lets you do things without thinking. The are responses that are very quick and automatic and they protect you. They use neurone pathways called reflex arcs where a sensory neurone directly controls a motor neurone. Reflex arcs bypass the brain so you don't decide what to do. Reflex arcs make you automatically blink if something gets in your eye or makes your pupils in your eyes get smaller in bright light.

B1 Skin and receptor cells

Your skin can detect many different stimuli, including touch, heat, cold, pain and pressure. Remembering THCPP might help you learn the different stimuli.

For each of these stimuli you have different receptor cells. The cells are adapted to become specialised cells to detect different things.

B1 Sensitivity

Are you a sensitive person? You are - we all are!

We all have sense organs which detect changes inside and outside the body. This is not just your five senses, sight, smell, hearing, taste and touch (SSHTT) - but other things like heat and cold, pain etc.

Now then you sensitive person, anything that you are sensitive to is called a stimulus. It stimulates you. You detect the stimulus because your sense organs contain receptor cells. So, back to homeostasis, your skin has receptor cells to detect changes in temperature. Hopefully you have worked out that this leading up to the nervous system.

These receptor cells make electrical signals called impulses. These usually go to the brain, unless it is a reflex action,. The brain then sends impulses to other organs or muscles to make the changes that the body needs to stay the same - back to homeostasis again eh?!

So what happens. Well the electrical impulses travel along neurones (or nerve cells). This movement of impulses is called neurotransmission. This links up nicely to how drugs called stimulants speed up the neurotransmissions. Now if you look at the diagram below, it has a cell body and long extension bits that look like tentacles (but they are not). These are called dendrites and they receive impulses from the receptor cells or other neurones. The impulse then moves along the dendron to the axon. Here it then goes to other neurones and so on.

So, the receptor cells receive the impulse and sends it along the axon. If the receptor cells are damaged no signal is got so no impulse is sent.

Remember that you are a big organism and there are millions and millions of neurones. Groups or bundles of these neurones are packed together into nerves. We are vertebrates and so we have an organ called the spinal cord. The spinal cord contains many nerves packed together and this connects to the brain. The brain and the spinal cord together make up the central nervous system (CNS) which controls your body.

B1 Homeostasis

This is a big topic and lends itself to questions worth a lot of marks.

So, what is homeostasis?

Well the, homeostasis is where the conditions inside the body are kept the same. It is all about keeping the internal environment the same regardless of what is happening.

There are 3 main things that you need to know how they are controlled.

1. Water - osmoregulation.
2. Temperature - thermoregulation.
3. Glucose - Blood glucose regulation.

Basically, water is to do with your sweat glands, kidneys and urine. Temperature is to do with your skin, sweating and blood vessels and glucose is about your pancreas and liver.

But, and it's a big but, you have to learn the various diagrams that go along with these 3 things to control. So let's start with water control.

You lose water by breathing and sweating. You also lose water in urine. If you drink too much water then your kidneys will produce more dilute urine - obviously. If you do not drink enough water then you will produce less urine and your brain tells you that you are thirsty. Again, common sense really.

Now, thermoregulation is a big topic to learn and you must include the diagrams that show what the skin does when you are hot or cold. Your body works best at 370C which is the optimum temperature for many chemical reactions and enzymes to work. Your body under the control of the hypothalamus which is a small part of the brain that monitors temperature.

So, what happens then?

When you are cold:

1. The hypothalamus causes muscles to shiver. This makes heat which warms you up.
2. The hypothalamus also causes erector muscles in the skins dermis to contract. This causes the skin hairs to stand up. This traps a layer of air for insulation. Note: it traps air not eat!
3. The hypothalamus constricts the blood vessels called capillaries near the skins surface. This means that less warm blood is near the surface so you lose less heat to the air. The fancy word for this is vasoconstriction.

When you are warm:

1. The hypothalamus causes sweating. You use heat to evaporate the sweat and so you cool down.
2. The hypothalamus increases the amount of blood flow to the blood vessels - capillaries - near the surface of the skin. I does this by making the blood vessels wider, it dilates them, so more warm blood flows near the surface of the skin so more heat is lost to the air - so you cool down. This is called vasodilation.

                                                Vasoconstriction                  Vasodilation


Diagram of the skin

Note where the sweat gland, capillary and hair is.

Negative feedback.

The control of body temperature is an example of negative feedback. This means that if you get too hot your body will work to make it colder, and if your are too cold then your body will make it warmer. All this, remember, is under the control of the hypothalamus and it is happening all the time without you thinking about it.

B1 Genetic disorders

What is a genetic disorder? Well, basically it's a disease caused by faulty alleles. Remember, alleles are the 2 different forms of the genes so if these are altered then the genotype and phenotype could be altered. This is not important if it means that you can't roll your tongue or you haven't got an ear-lobe! It is important if you end up with sickle cell disease or cystic fibrosis.

Let's work out how you can get these disorders, no, I am not going to call it a disease 'cos you can't catch it like a bacteria, fungus or virus. You don't get it from someone sneezing! You get these disorders from faulty alleles passed down to you from your parents. Remember though, it is all down to probability. It's the chance that someone has of getting the disorder from their parents alleles.

So, what is the chance? Well, sickle cell disorder and cystic fibrosis are both caused by faulty alleles which are recessive. This means that you have to get 2 copies of the recessive allele to get the disorder. You have to get one copy of the allele from your mum and one copy for the allele from your dad. As it's recessive, if you only get one copy of the allele then the other would be dominant therefore you wouldn't get the disorder. You would however still carry the recessive allele so you would be a carrier.

Sickle cell disorder

Sickle cells results in the red blood cell being a sickle shape - these are the pink banana shaped cells in the photograph. The sickle cell is caused by a mutation in the haemoglobin. Haemoglobin is the pigment in the red blood cell that carries Oxygen so these mutated cells can carry less oxygen that the normal red blood cells which are bi-concave shaped. The sickle cells are also not as flexible as normal red blood cells so sometimes get stuck in blood vessels.

Symptoms of sickle cell
People with these disease easily become tired and short of breath because they cannot carry enough oxygen around their body for respiration.

They also have at times very painful joints because the sickle cells have stuck together and blocked some blood vessels - this could be fatal!

Cystic fibrosis symptoms

This is another disorder caused by a recessive allele. Remember you must get 2 recessive alleles to get this disease - just like Sickle Cell disease. So it's people who have 2 copies of these diseases who suffer from it.

In cystic fibrosis the lungs get clogged up with thick mucus. This makes it difficult to breathe. The mucus also traps pathogens which leads to infections. This thick mucus will also block some of the tubes that carry enzymes to the small intestine. Remember, enzymes break down large molecules in food into smaller molecules. Example, proteins are broken down into amino acids. If you are not absorbing enough nutrients then you will not put on weight.

Family pedigree charts

Doctors create pedigree charts like the one above to show how a genetic disorder is inherited and to show how the disease is passed on through the family. They can then work out the chances, the probability that a person may inherit this disease. This is called a Pedigree analysis. They could also inform parents of the probability of them passing on the disease to future children. This would help them decide if they want to have babies or not. What a horrible decision to have to make eh?!

B1 Explaining inheritance - Punnett squares

Punnett squares are also called Genetic diagrams. Useful for showing the probability of organism getting a certain allele. Who cares - you might say. Well it is useful not only for plant breeders but for working out the probability of someone giving birth to a baby with a genetic disease like sickle cell disease or cystic fibrosis.

Look at the example of the flowers Both parent flowers have the same phenotype and genotype. Thet are both phenotype purple and genotype Bb.

Notice, that one of the flowers is white. That is because it has received one recessive white allele from the pollen and one recessive white allele from the egg.

This gives it a probability of 1/4 = 0.25 being white or 0.25 X 100 = 25%

B1 Explaining inheritance

It all started a long, long time ago.

An Austrian monk in 1865 called Gregor Mendel put forward his ideas on genes and alleles. He did all his research on pea plants and actually grew over 29,000 plants!

Back to the beginning - again!

Plants and animals produce sex cells, these sex cells are called gametes. The male gametes in animals are called sperm cells and in plants they are called pollen grains. The female gametes in both plants and animals are called egg cells.

A huge difference between sex cells and body cells ( body cells are all the other cells) is that the sex cells have only one copy of each chromosome and therefore only one allele for each gene.

But why have they only got one copy - well let's think about human beings. All our body cells have 23 pairs of chromosomes which is 46 chromosomes. Remember, we get 1/2 our chromosomes from mum and 1/2 from dad. So, if the sperm has 23 chromosomes and this joins or fuses with an egg cell which also has 23 chromosomes then the fertilised egg or zygote now has 46 chromosomes or 23 pairs.

23 + 23 = 46 obviously!

Now, there are a lot of fancy words to learn and understand here - but once you get them it is all really easy - honest. Let's go back to genes. Each gene has 2 alleles. Now, imagine that a flower can be one of 2 colours - red or white. If a pure bred red flower gives its pollen to fertilise the eggs of a pure bred white flower then the flowers grown from the seeds are always red. This is because the flower receives 2 alleles for flower colour - one for red and one for white. The white flower allele has no effect if the red colour allele is also there. The red colour in this case is said to be dominant and the white colour is said to be recessive. The white colour for this flower can only happen if it gets the recessive alleles for white form both parents.

When,drawing diagrams to predict what will happen we use letters to represent the alleles. A capital letter is always used to represent the dominant allele and a small letter for the recessive one. In this example let's use R for the dominant red colour and r for the recessive white. Oh, and don't forget, the alleles are in pairs so the pair of alleles a flower could have would be, RR, rR, Rr or rr. Rr and rR are classes as the same.

RR must be red as it only has the red alleles.

Rr also must be red because even though it has the white r allele, this is masked by the dominant R allele.

rr must be white because it only has the white allele.

Time for some more fancy words here.

The alleles in any organism make up its genetic makeup and so is called the genotype.

What the organism looks like is called the phenotype.

So, RR is the genotype and the phenotype is of a red flower.

and, Rr is the genotype and it the phenotype is also of a red flower - (R is dominant to r).

rr is the genotype and the phenotype is of a white flower (there are only r alleles)

Notice the different genotypes that can produce the same phenotype.

If both alleles are the same, like RR or rr, then the organism is homozygous.

If both the alleles are different, like Rr, then the organism is heterozygous.

B1 Genes

Jeans for genes sounds familiar. This is where you wear jeans to raise money for research into genes.  But what are genes, where are they found and what to they do?

Well, lets start at the very beginning, let's zoom in on a cell.

First of all, you must be able to draw and label a plant and animal cell.

Inside the nucleus there are long strands of DNA. 

Each strand forms a chromosome.
Now chromosomes are divided up into genes.

So the chromosomes are found inside the nucleus. The nucleus contains different chromosomes and these are arranged in pairs. Humans have 23 pairs of chromosomes. Notice in the diagram below the chromosomes at the end are an X and a Y. This tells you that this is a male. If there were 2 X chromosomes it would be a female.

Different chromosomes contain different genes and each gene does a particular job. Eg. many of these genes control what we look like, hair and eye colour, ear lobes etc.

Variation caused by genes is called inherited variation - yes it's back to variation again! This is because we inherit our genes from our parents, 1/2 from mum and 1/2 from dad.

So genes carry the code or instructions for a certain characteristic. Some genes for the same characteristic may have 2 slightly different versions which give slightly different instructions to make differences and variations. These different forms of a gene are called alleles. There are different alleles for your eye colour eg. brown or blue.

Summarising all this then, there are 2 copies of each chromosome in the nucleus and there are 2 copies of every gene that makes up the chromosome called alleles.

Exam tip - if you are asked about characteristics and genetic then talk about alleles not just genes.

B1 Evolution

Evolution. I think that was the name of a film. I know it was, about life that starts as a single cell and quickly evolves to flying like dinosaurs. Well, I enjoyed it. Now, back to evolution.

Evolution means 'a gradual change over time'

The names Charles Darwin usually springs to mind. He lived from 1809 - 1882. Scientists then realised that species can change over time but didn't really know why. Darwin, took all the various ideas about what happened and with his own research and ideas and came up with his theory of Natural Selection. He published his theory in a book called On the Origin of Species by Means of Natural Selection. 

So, what's it all about then. Well, back to variety and variation. Let's think of a the ancestor of the giraffe. It didn't always have a long neck and was probably like a little deer. Now, a group of these animals would show some variation - they would all be slightly different. Maybe, some of them had a slightly longer necks than others. Can you see where this is going. Now, imagine that there is some sort of drought. The grasses die out but trees survive because they have longer roots. The giraffey things that have the slightly longer necks can reach the leaves on the trees and so they survive. The ones with the slighter shorter necks cannot and so  die. This means that the ones that survive can breed and pass on their characteristics - alleles - to their offspring. This is Survival of the fittest. Over a period of time the population will change to have loner necks. Any species that haven't adapted to an environmental change will die out and become extinct. 

It could also apply to predators. A lion has a litter of cubs. The strongest one has the best chance of surviving. Survival of the fittest.

Now, don't think that evolution is all to with animals in the past - you know, dinosaurs and all that. 

Evolution is happening all the time! Rats are now resistant to a poison called warfarin.Warfarin is a poison that stops the rats blood from coagulating. When it was first used most of the rats died, but some survived because of variation - they were slightly different. These survivors bred and now all the rats are resistant.

Darwin, when on his travels to the Galapagos Islands noticed that the finches, a type of bird, on the different islands all kind of looked the same but they all had slightly different beaks. He worked out that originally they were all one population of birds on one island. Maybe a storm or something blew them all onto different islands. As the birds were originally slightly different due to variation then maybe as the islands were all slightly different then different birds would survive and breed on different islands. There is a lot of differences there eh?! Over time, these survivors on each island would breed and eventually become so different that they couldn't interbreed with birds from other islands.

Survival of the fittest.

They had become a new species  - this is called speciation.

B1 Reasons for variety

Why are species all so different? Wouldn't it be easier if they were all the same? No it would not, it would also be extremely boring, scary even. Think if every species, even humans were exactly the same as each other.

Aaaahhhh!!!!!!!!

All organisms are adapted to their surroundings. They have all these variations so -  they can survive in whatever habitat that they are living in.

There are a few specific animals that you must know about.

1) Sharks. Don't just think of the obvious bits, like streamlined shape to move fast and catch their prey, or sharp teeth to catch and kill their prey. Shark tissues contain TMAO - ( this stands for trimethylamine N-oxide if you are interested - but you don't have to know it) Anyhow, TMAO is poisonous to humans in high concentrations - so don't go to your local chippie and ask for shark and chips please! But wait, why would a shark evolve to be poisonous to human beings? We didn't evolve to be a predator of sharks! Here's clue. Greenland sharks, found in the Arctic Ocean, which is pretty cold, OK very cold, contain much higher amounts of TMAO than other sharks. Why? It;s because TMAO happens to be a natural antifreeze and just happens to be poisonous to us by the way.

2) Polar bears. Yes, all right we all know its got white fur for camouflage and maybe the thick fur and blubber for insulation. You might even know already about it having large feet to spread out its weight - reduces the pressure on the snow and ice or even that it has got rough soles on its feet to grip the ice. But, did you know that it has small ears to reduce the heat loss? Did I mention the sharp teeth?

3) The final animal is the Pompeii worm. Yes, I admit it. It's not exactly a well known beastie is it - but it is a survivor and a great example of the variety of organisms. So, what's so special about this worm. Well, mainly it has adapted to live near deap-sea hydrothermal vents. Here, hot water at temperatures of more than 350 oC come out of the vents and cool quickly. This is at depths of over 2km where it completely dark with high pressures, over 200 times those at sea-level. This worm spends a lot of its time inside a papery tube to protect itself from predators. It is covered in a thick layer of bacteria, that helps protect it from the heat. It can also survive the great pressure. It also has no eyes 'cos it's so dark if it had it wouldn't be able to see anything anyway!

B1 Continuous or discontinuous variation

Not more variation - well only as wee bit more.

We can divide variation into two types.

Continuous variation or discontinuous variation.

I hope by now that we all now that there is a big amount of variation between the same species and between different species.

Continuous variation is where there is a complete range of differences example height. Humans are not either short or tall, they can be anything in between. There is a continuous range of heights. If you drew a graph of this it would be a normal distribution curve. Characteristics that show continuous variation are often controlled by both genes and the environment. Example, you may inherit the alleles that may make you tall but unless you have the correct balanced diet you might not. If you don't grow tall, but you could have then this is called an Acquired characteristic. Acquired characteristics are caused by the environment and so are cause environmental variation between organisms. Makes sense to me.

Discontinuous variation is where there is a definite fixed value. You are either one thing or another. Your blood group is an example of discontinuous variation. You are one of 4 groups, A, B, AB or O. That's it - you must be one of those 4 goups and not nearly one or have a bot of 2 or ........ . You could draw this as a barchart. Discontinuous variation is usually caused by changes in the DNA so it is called Genetic variation.

B1 Variation

What is variation? Differences in characteristics are called variation.

There is variation within a species but obviously much more variation between different species. Think of the variation between dogs which are the same species. There are lots but then think of the variation between a dog and an elephant - lots more differences. Yes, I know it's obvious and probably a stupid example but it makes the point - I hope!

Variation makes it hard to classify animals and plants and to decide if they are different species. So, how do they do it? Well, if someone finds what they think is a new species, that is not enough to actually say that it is a new species. Say I found a new bat - I think I will call it Batty glover. Note, the Genus is Batty and the species is glover. This one bat may be just a one off hybrid so I would have to find some more. Then I could see if these new bats were different enough from other bats but themselves pretty similar to be called a new species. Guess there will not be a Batty glover yet!

Finally, all this classification stuff. Variation, Kingdoms and all that - what is the point? Why bother?
Is this just something to keep scientists in a job? Well no it isn't - honest it isn't.

It is important to classify organisms using the binomial system because it allows biologists to:

1) easily identify new and existing species.

2) see how organisms are related.

3) identify areas of greater and lesser biodiversity.

Typical teacher - explaining it nicely and then throws in a big new word. What is biodiversity?

Biodiversity is a measure of the total number of different species in an area.

What has that got to do with anything? Well, it's really very important. We get lots and lots of many different and important products like food and medicines from living things. The more species there are, the more things we have to discover new products. That sounds pretty selfish, we are just identifying them so we can use them. Probably true but on the positive side if we need them then there is more chance that we will look after them and conserve them. Biodiverse areas are more likely to recover quicker from a natural disaster like flood, drought or fire than a less diverse area because there are more species that could survive and breed. Many biologists also think that as countries and governments only spend so much on conservation that if they can identify areas where there is a large biodiversity  - which they call a biodiversity hotspot - then governments could first of all concentrate on these areas because they could save a greater number of species. Pity we can't save them all though but it's down to time and money.