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Biology B1 (Exchanging surfaces + substances (Exchange surfaces are…
Biology B1
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Bacterial Cells
Bacteria are Prokaryotes
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Bacterial cells don't have a 'true nucleus' - they have single circular strand of DNA that floats freely
Parts of an animal cell
Nucleus
Contains genetic material, which controls the activities of the cell
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Cytoplasm
Most chemical processes take place here, controlled by enzymes
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Stem Cells
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Medicine already uses adult stem cells to cure disease. For example, stem cells transferred from the bone marrow of a healthy person can replace faulty blood cells in the patient who receives them.
Embryonic stem cells could also be used to replace faulty cells in sick people - you could make insulin - producing cells for people with diabetes, nerve cells for people paralysed by spinal injections and so on.
In a type of cloning, called therapeutic cloning, an embryo could be made to have the same genetic information as the patient. This means that the same genes and so wouldn't be rejected by the patients body if used to replace faulty cells.
However, there are risks involved in using stem cells in medicine. For example, stem cells grown in the lab may become contaminated with a virus which could be passed on to the patient so make them sicker.
Stem cells and plants
In plants, stem cells are found in the meristems (parts of the plant where growth occurs)
Throughout the plants entire life, cells in the meristem tissues can differentiate into only the of plant cell
These stem cells can be used to produce clones (identical copies) of whole plants quickly and cheaply
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Stem cells can also be used to grow crops of identical plants that have desired features for farmers, for example, disease resistant
Against stem cells?
Some people are against stem cells research because they feel that human embryos shouldn't be used for experiments since each one is potential life.
Others think curing existing patients who are suffering is more important than the rights of embryos
One fairly convincing argument in favour of this point is that embryos used in research are usually unwanted ones from fertility clinics which, weren't used for research, would probably just be destroyed. But of course, campaigned for the rights of embryos usually want this banned too.
These campaigners feel that scientists should concentrate more on finding and developing other sources of stem cells, so people could be helped without having to use embryos
In some countries stem cells research is banned. Its allowed in the UK as long as it follows strict guidelines.
Chromosomes and Mitosis
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The Cell Cycle
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Body cells in multi-cellular organisms divide to produce new cells as part of a series of stages called the cell cycle
The end of the cell cycle results in two new cells identical to the original cell, with the same number of chromosomes.
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Mitosis
Once its contents and DNA have been copied, the cell is ready for Mitosis...
The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell
Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells - the nucleus has divided.
Lastly, the cytoplasm and cell membrane divide
The cell has now produced two new daughter cells. The daughter cells contain exactly the same DNA - they're identical. Their DNA is also identical to the parent cell.
Microscopy
Electron Microscopes
Uses electrons to form an image. Higher magnification. Higher resolution (the ability to distinguish between two points - sharper image). Sees smaller things like internal structure of mitochondria and chloroplasts
Light Microscopes
Uses light and lenses to form an image and magnify it. Sees individual cells and large sub-cellular structures, like nuclei
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Parts of a plant cell
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Chloroplasts
Contains Chlorophyll, which absorbs light energy for photosynthesis
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Diffusion
Diffusion is the SPREADING OUT of particles from an area of HIGHER concentration to an area of LOWER concentration
Diffusion happens in solutions and gases. The BIGGER the concentration gradient (the difference in concentration, the faster the diffusion rate
Dissolved substances can move in and out by diffusion. Only very small particles such as oxygen (respiration), glucose, amino acids and water.
Particles in the membrane flow through the where a higher concentration to where there is a lower concentration.
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The larger the surface area of the membrane, the faster the diffusion rate, because more particles pass through at once.
Active Transport
Active Transport is the absorption of substances against the concentration gradient i.e. from lower to a higher concentration
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Minerals should move out of the root hairs if they followed the rules of diffusion. It allows the plant to absorb minerals from a very dilute solution, against a concentration gradient.
Essential for growth. Needs ENERGY from respiration to work. Happens in humans too, taking glucose from the gut and from kidney tubules.
Active transport is used in the gut when there is a lower concentration of nutrients in the gut, but a higher concentration of nutrients in the blood.
When a lower concentration of nutrients in the gut than in blood - the concentration gradient is the wrong way
Active transport allows nutrients to be taken into the bloodstream when its concentration in the blood is already higher than the gut. Then it is used for respiration when transported to cells.
Osmosis
OSMOSIS is the MOVEMENT of WATER MOLECULES across a PARTIALLY PERMEABLE MEMBRANE from a region of HIGHER CONCENTRATION to an area of LOWER CONCENTRATION
A partially permeable membrane has small holes in it (small enough for tiny molecules (like water) can pass through and bigger ones (like sucrose) can't.
Water molecules pass through both sides (move randomly). More water molecules on one side than another = steady net flow i.e. stronger sugar solution
This means stronger solution gets more dilute. "Evens up" the concentration either side of the membrane.
Osmosis is a type of diffusion - passive movement of water particles from an area of high to low concentration.
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