Cells
Learn all about cells with these GCSE biology revision videos. Revise how cells are structured, how they divide and how we can see them. We'll also explain the main differences between optical, light, and electron microscopes.
Stem cells: Where they come from and how they are used in humans and plants.
Narrator: We're all very complex organisms, made up of lots of different types of cells carrying out different jobs in our bodies; such as nerve cells, blood cells, fat cells and muscle cells.
So, where do they all come from? Each one of us starts off as a single cell when an egg and a sperm join together. This then divides by mitosis to form two identical cells, and they just keep on dividing to form a hollow ball of 200–300 tiny cells.
Now – the clever bit. The cells on the inside layer of this very early embryo can make all of the cell types needed in your body. They're called stem cells.
The stem cells continue to divide by mitosis, and so the embryo grows. They also start to differentiate,to become specialised for different purposes. For example, red blood cells look very different from nerve cells, but they both start out as embryonic stem cells.
Adults don't have any embryonic stem cells, but they do still have stem cells – they're essential for replacing or repairing normal cells which become damaged, or worn out. But the adult stem cells are more limited in the types of cell they can make. For example, bone marrow stem cells only form different types of blood cells.
Plants have stem cells too. They're found at the meristems, the growing tips of the roots and the shoots. The big difference is that the stem cells in adult plants can still make every type of plant cell. Each one has the potential to form a whole new plant!
Unsurprisingly, people want to make use of these amazing cells. Plant stem cells can be used to make clones, identical copies of the parent plant. That's massively useful for lots of things, like producing orchids and other house plants quickly and cheaply, conserving endangered species, or making clones of plants that have been genetically modified to deal with environmental stresses.
Using plant stem cells is one thing. Using human stem cells in medicine is quite another. Scientists have found ways to grow embryonic stem cells in the lab, and are trying to use them to cure conditions such as diabetes (by replacing the insulin-producing cells in the pancreas), or enable people paralysed by spinal injuries to walk again by regrowing spinal nerves.
The clinical challenge is to encourage the embryonic stem cells to develop into the type of cells we need, without them growing into what we don't want.
It's ethically tricky too, because the stem cells come from human embryos.
Adult stem cells offer another possible route. Scientists have been using them for years in bone marrow transplants. And they are now investigating different types of adult stem cells, and how they might control the way they develop.
After years of research, scientists seem to be on the brink of success with a number of stem cell treatments which could change medicine forever.
Watch this space!
Specialisation: Cells, such as red blood cells, adapted for particular jobs within a multicellular organism. Organisation of tissues into organs and systems.
Diffusion: Movement of particles according to their concentration, how this happens in living cells, and why there is an upper size limit.
Microscopy: The main differences between optical, light, and electron microscopes.
Infection and response
Learn all about health and infection - and how the body fights against it. We'll explain different diseases, what causes foodborne illnesses, and the body's defence mechanisms.
Diseases: Prevention and treatment of malaria, which is spread by mosquitoes, and the sexually transmitted diseases chlamydia and HIV.
Foodborne illness: Four major safety precautions to inhibit the growth of bacteria such as salmonella and E. coli in cooked food.
Monoclonal antibodies: Their uses in disease detection and treatment. How they are mass produced from mouse lymphocytes and tumour cells.
Non-communicable diseases: Examples of diseases arising from environmental and lifestyle risk factors.
The body's defence mechanisms: How mucous membranes, skin and clotting factors keep diseases out, while the immune system fights any that get in.
Body systems
In this set of biology revision videos, learn about some of the processes in the human body that ensure it functions correctly. Let's learn about the impact of exercise, sex hormones and puberty, eye anatomy, and the menstrual cycle phases.
The impact of exercise: How the circulatory system improves with regular exercise.
Sex hormones and puberty: How testosterone from the testes and oestrogen from the ovaries cause physical changes, from breast growth to body hair.
Mechanics of breathing: How the muscles of the respiratory system function to allow inhalation and exhalation.
Eye anatomy: How the human eye focuses light rays onto the retina, and how this can go wrong in short- and long-sighted people.
Blood glucose: The endocrine system maintains steady blood sugar levels. Diabetes disrupts this balance and must be managed by the patient.
Diabetes is a disorder where the body can't control its glucose concentration.
Glucose is the main energy source for all the cells of the body, so it's kind of important to keep its concentration right.
It's produced from the digestion of carbohydrates, so every time you eat something, it's absorbed into the bloodstream.
The blood is always carrying glucose, so it's available for cells as and when they need it.
The amount of glucose going into your body, and the amount you’re using changes through the day.
So the concentration of glucose -or blood sugar - changes all the time.
But if the concentration gets too high the glucose becomes dangerous and starts damaging cells, tissues and organs.
And if it gets too low your cells can't function properly.
So there has to be a glucose control system, and that's where insulin comes in.
Insulin is a protein hormone made in the pancreas and carried around the body in the blood.
The pancreas cells are sensitive to the blood sugar concentration, so as soon as it starts rising they release more insulin into the blood.
That Insulin acts like a switch, allowing cells to absorb more glucose.
The Insulin also affects your liver cells.
Liver cells convert excess soluble glucose to an insoluble carbohydrate called glycogen which is stored in the liver and the muscles.
That’s what happens when the blood glucose concentration rises, so what about when it drops?
Well, your pancreas releases less insulin, and your liver and muscle cells remove less glucose from the blood.
Glycogen may be converted back into glucose within the liver cells, and released into your blood.
Or Glycogen can also be converted back into glucose in your muscle cells they use it themselves.
So, the body's always maintaining a delicate balance, keeping glucose levels in a safe range and if that balance goes wrong, that's diabetes.
There are two types of diabetes, and they're called…'type 1'… and… 'type 2'. It's really original, right?
The symptoms are similar, but the causes are different.
Type 1 diabetes is when the body's immune system attacks the pancreas, destroying the cells which produce insulin.
If someone has type 1 diabetes they have to inject themselves with insulin, to replace the insulin that their body can't make.
And if it is untreated, the blood glucose levels just keep rising.
They have to monitor their blood glucose concentration regularly be aware of what and how much they've eaten, and how much exercise they've done.
Type 1 affects a relatively small percentage of the population, often young people and researchers don't yet fully understand the causes.
Type 2 diabetes is much more common.
It's caused by the effects of cells in the body becoming resistant to insulin so much so that the pancreas can't compensate, however much insulin it takes.
Someone is more likely to develop type 2 if other members of their family have it.
Other factors increase the risk too though such as age, and there's also weight: 80 to 85% of people with type 2 are obese.
A lack of exercise and an unhealthy diet are therefore major risk factors.
The good news on that is that by losing weight, eating carefully and exercising, many people can completely reverse the problem.
In the most severe cases Insulin injections are needed.
Understanding diabetes really is important, because the numbers of people affected by it are rising at an alarming rate.
But hopefully if we encourage people to eat well and exercise more, we can get it under control.
Menstrual cycle: The sequence of four hormones, from the pituitary gland and ovaries, that coordinate ovulation with changes in the uterus lining.
Osmoregulation: How the human body manages blood concentration through filtering and reabsorption in the kidneys, controlled by the pituitary gland.
Genetics
Watch this biology revision collection to find out about genes, DNA and genetic inheritance. Let's learn about the structure of DNA, what meiosis is, and more!
Genetic disease: Descriptions of the inherited diseases cystic fibrosis, Huntington's and haemophilia, along with the chromosomal disorder Down's syndrome.
Protein synthesis: Mechanisms used by ribosomes in cells to make proteins, according to instructions from the DNA in the nucleus.
Genetic engineering: How DNA is altered to make bacteria produce insulin for the treatment of diabetes in humans.
Structure of DNA: The sequences of base pairs that code for specific amino acids.
Meiosis: The process unique to sexual reproduction that creates sex cells to allow the DNA of both parents to be combined.
Genetic inheritance: How dominant and recessive alleles are tracked through different generations, using cats as an example.
Plants and their structures
Improve your GCSE biology knowledge by learning what photosynthesis is and how plants are structured in this collection. You can also learn about phototropism and gravitropism.
Rate of photosynthesis: Factors that limit photosynthesis, particularly light, water and carbon dioxide, and an experimental demonstration.
Phototropism and gravitropism: Growth hormones called auxins make different areas of a plant grow towards or away from light, and similarly with gravity.
Plants need to respond to the world around them just like we do, and for them, two of the most important things are gravity and light.
They need to figure out which way is up and which is down, and they need to know where the light is so they can photosynthesise. So how do they do that?
Well, mainly they use hormones. In particular, a group of plant hormones called auxins.
Auxin controls growth in the meristems near the tips of the shoots and roots causing shoot cells to grow more and root cells to grow less.
So… the pattern of auxin distribution around the plant is really going to change the way it grows.
If a plant tip had loads of auxin on the left side and hardly any on the right, the left side would grow way more than the right and we'd end up with a very lopsided plant.
It looks weird but it does happen, and it's a really important process.
Plants need to respond differently to light depending on where it’s coming from to help them maximise photosynthesis.
When light falls evenly on the shoot, the auxin spreads evenly through the shoot tip – and it grows steadily up.
But when a shoot tip is exposed to light from just one side auxin diffuses away from the light to the shady side.
So the cells on the shady side elongate and grow faster, and the shoot grows towards the light.
This response is called positive phototropism.
You get the opposite, negative phototropism too - think of the roots, they're negatively phototropic because they grow away from light.
The other major factor that determines how plants organise their growth is, of course, gravity…
When a root starts to grow out of a seed it needs to turn down WHICHEVER way the seed’s been planted…
How does it do it? Yep you bet, auxin.
The auxin sinks to the lower side of the root in response to gravity
But remember, auxin in roots slows down the rate of growth – so the cells on the lower side grow more slowly and this creates a downward bend, which, if you're a root, is just the sort of bend you want.
If a shoot starts growing sideways, gravity again causes an unequal distribution of auxin with more on the lower side of the tip.
This has the opposite effect to the roots, making the cells grow faster and bending the shoot upward.
The way plants respond to gravity is called 'gravitropism'.
Roots are positively gravitropic so they grow downwards, and shoots are the opposite - negatively gravitropic.
Auxin is really important in another way too it affects the overall shape of the plant.
See, it's essential that the central shoot grows more quickly, and stays stronger, than the side branches that grow out of it.
And that's all down to good old auxin.
Transport system in plants: The flow of water upwards through xylem in the stem and the transportation of glucose throughout the plant by the phloem.
Living processes
Many processes happen in the human body to ensure it functions correctly. Find out more about some of them in this collection of biology revision guides about food and nutrition, enzymes, and the human excretory system.
Food and nutrition: The importance of carbohydrates, fats and proteins to the body.
Enzymes: How their active sites are structured to match their substrate in a lock-and-key model, and how inhibitor molecules can slow the process down.
Human excretory system: The function of the kidneys in removing water and dissolved waste while preserving useful substances by reabsorption.
Biodiversity
Learn about what biodiversity is (the variety of plant and animal life in a particular habitat) in this revision collection and explore facts about deforestation, eutrophication, and biodiversity investigation.
Deforestation: Its negative impact on biodiversity and the climate, and how some countries have begun to manage logging to minimise the damage.
Eutrophication: The overgrowth of plants caused by pollution from excess fertiliser and why this is a bad thing.
Biodiversity investigation: A practical experiment to measure organisms in a field. Biotic and abiotic factors affecting distribution.
