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Edexcel Biology Topic 1 & 2 (Key concepts in Biology (Quantitative…
Edexcel Biology Topic 1 & 2
Key concepts in Biology
Cells
Eukaryotic cells are more complicated and have a nucleus, for example, animal or plant or fungi cells.
Prokaryotic cells are smaller, simpler and don't have a nucleus, for example bacteria.
Animal cell features
Cell membrane- controls what enters and leaves the cell
Nucleus- controls the cell's activities but also holds the cells genetic information
Cytoplasm- gel-like substance where most of the cell's chemical reactions takes place.
Ribosomes- site of protein synthesis, makes proteins for the cell
Mitochondria- site of respiration, makes and stores energy for the cell
Plant cell features
Cell membrane- controls what enters and leaves the cell
Nucleus- controls the cell's activities but also holds the cells genetic information
Cytoplasm- gel-like substance where most of the cell's chemical reactions takes place.
Ribosomes- site of protein synthesis, makes proteins for the cell
Mitochondria- site of respiration, makes and stores energy for the cell
Cell wall- gives the cell support, made of cellulose
Vacuole- controls the cell's pressure, stores water and waste and also contains cell sap.
Chloroplasts- site of photosynthesis, contains chlorophyll which is the green pigment in plant's leaves. They also make food for the plant.
Bacteria cell features
Flagellum- long whip-like structure that rotates to aid the cell in movement
Plasmid DNA- small loops of extra DNA and are not part of the chromosome. Plasmids contain genes for things such as antibiotic resistance and can be passed between bacteria.
Chromosomal DNA- contains information for the cell's genetics and activities.
Cell wall- gives the cell support
Ribosomes- makes proteins for the cell
Quantitative units
Milli- 1x10^-3
Micro- 1x10^-6
Nano- 1x10^-9
Pico- 1x10^-12
Femto- 1x10^-15
Kilo- 1x10^3
Mega- 1x10^6
Giga- 1x10^9
Tera- 1x10^12
Peta- 1x10^15
Specialised cells
Egg cells (ovum)
Haploid nucleus- so when it is fertilised the zygote has the right amount of chromosomes.
Cytoplasm- contains nutrients and mitochondria needed for mitosis after fertilisation.
Cell membrane- changes after fertilisation so only one sperm can get through
Sperm cell
Haploid nucleus- so when it fertilises the egg, the zygote has the right amount of chromosomes.
Acrosome- enzymes that allow it to get through the ovum's cell membrane
Mitochondria- makes and releases energy needed for the sperm's journey to the Fallopian tubes.
Tail- helps the cell's mobility
Ciliated epithelial cell
Cilia- little hairs that trap dust and microbes and waft them out of the breathing system
Cells and control
Cells and processes
Mitosis
Interphase- DNA duplication and the making of sub-cellular structures such as ribosomes.
Prophase- Nuclear membranes start to break down and spindle fibres appear.
Metaphase- Chromosomes line up along the equator of the cell attached to the spindle fibres by their centromere.
Anaphase- Each pair of chromosomes splits and the separate ones go to each pole of the cell by the spindle fibres.
Telophase- Nuclear membranes start to form around the poles and spindle fibres disperse.
*Cytokinesis- Cell surface membranes form to make two genetically identical daughter diploid cells.
Mitosis is used in growth and repair in organisms by producing new cells.
It is also used in asexual reproduction in plants which is essentially just cloning of cells as there is only one parent and no mixing of gametes
Mitosis produced two genetically identical diploid daughter body cells
Cancer is the uncontrolled cell division by mitosis. It causes lumps or growths of cells as mitosis has occurred uncontrolled by the body because of a mutation.
Cell differentiation
The process in which a cell changes or adapts to become specialised for it's job. This happens in animal and plant cells.
Cell differentiation is really important in the development of specialised cells as we wouldn't be able to perform a lot of our functions without specialised cells.
Cell elongation
This is where a plant cell expands making the cell bigger so it can grow. This only occurs in plants
Cell division
Happens by mitosis. Happens in plants and animals.
Stem cells and the Brain
Stem cells are unspecialised cells that can specialise into any cell type depending on the type. Embryonic stem cells can differentiate into any type of body cell however adult stem cells can only differentiate into certain cell types eg. blood cells.
Meristems are a group of cells at the tip of each root and shoot that can continue to differentiate through the plants life so it continue to grow unlike animals who tend to stop growing after the first few years of life.
Stem cells are controversial in medicine as many don't agree due to the fact that they are from a foetus and are a potential human.
Main structures of the brain include: the cerebrum, the cerebellum, the medulla oblongata and the spinal cord.
The function of the the cerebral hemispheres is that the left hemisphere controls the right side of the body and vice versa. The cerebrum is responsible for lots of things including vision, language and memory.
The medulla oblongata is responsible for unconscious activities like heart rate and breathing rate.
The cerebellum is responsible for fine motor movements such as balance.
The spinal cord relays information between the brain and the rest of the body..
Key concepts in Biology
Enzymes
The active site of an enzyme is what gives it the high specificity as each enzyme has a complimentary substrate. Only one substrate can fit each enzyme.
Lock and Key Hypothesis- the enzyme is the lock and the substrate is the key. demonstrating the high specificity of enzymes as only one key can fit in a lock.
Enzymes can be denatured when the temperature is higher than 40 degrees or the pH is higher than optimum. Denaturing is the changing of the active site's shape due to environmental factors to a point where the substrate can no longer fit it. Thus making enzyme activity fall.
Enzymes are biological catalysts meaning they speed up chemical reactions in the body without being used up.
Enzymes in the body have an optimum temperature of around 37 degrees and get denatured at around 40 degrees. The optimum pH depends on the enzyme eg. pancreas lipase works best at 8pH but gets denatured past that point.
There is a point of saturation with enzymes where there are too many substrates for enzymes, every enzyme already has bound to a substrate therefore enzyme activity cannot increase any further.
Lipids- fatty acids and glycerol
Carbohydrates- sugars
Proteins- amino acids
Transporting substances
Osmosis
The movement of water particles across a semi permeable membrane from a region of high concentration to a region of low concentration, down a concentration gradient.
To work out the percentage change in the mass in osmosis when conducting an experiment you must first work out the difference between your masses. Then divide it by the original mass and multiply by 100. If it is a negative number then it is a decrease and if it is a positive number then it is an increase.
Diffusion
The movement of particles from a high conc. to a low conc. down a concentration gradient
Active transport
Uses energy from respiration to help the plant pull minerals into the root hair against a concentration gradient.
Microscopes
Electron
Specimen has to be dead
Greater magnification and higher resolution
Uses electrons to magnify
Allows you to see structures not visible to the naked eye.
Light
Uses light to magnify
Allows you to see structures not visible to the naked eye
Makes it easier to see how specialised cells function
Living material can be seen
Lower resolution and magnification.
Cells and control
Scanning
PET
PET Scanner use radioactive chemicals to show what part of the brain is active when the person is inside the scanner.
PET scans are detailed and show the structure a d function in real time.
CT
A CT scanner uses X-rays to produce an image of the brain
a CT scan shows main structures of the brain but not their functions. However if a CT scan shows a diseased or damaged brain structure and the patient has lost some function then the damaged area can be figured out.
The eye and neurones
Neurones
Sensory
One long dendron carries nerve impulses from receptor cells to the cell body which is located in the middle of the neurone.
One short axon carries nerve impulses from the cell body to the CNS
Motor
Many short dendrites carry nerve impulses from the CNS to the cell body
One long axon carries nerve impulses from the cell body to the effector cells.
Relay
Many short dendrites carry nerve impulses from sensory neurones to the cell body
An axon carries nerve impulses from the cell body to the motor neurones.
The axon carries signals away from the cell body while the dendron or dendrites carry impulses towards the cell body
Some axons have a myelin sheath which is an electrical insulator and speeds up the impulse
Synapses
A Synapse is a gap between two neurones.
When a nerve impulse arrives at the end of one neurone it triggers the release of neurotransmitter molecules from the synaptic vesicles.
The neurotransmitters diffuse across the synaptic cleft and bind with receptors on the next neurone triggering another impulse.
The receptor is specific to the neurotransmitter eg. acetylcholine, therefore will not bind to other chemicals.
The reflex arc is as follows:
Stimulus-Sensory Receptor-Sensory Neurone- CNS-Motor neurone-Effector-Response
The eye
The cornea focus' the light on the retina
The lens then fine tunes the focus
The iris muscles contract and relax to make sure the light doesn't damage the retina.
There are cells in the retina called rods and cones. Rods detect light intensity and cones detect colour
Eye conditions
Cataracts
Cataracts is when proteins build up in the lens making cloudy. You can fully treat it by replacing the ens with a plastic one
Longsightedness
This is when you can focus on far away objects but not on near ones due to your eyeball being too short therefore making the light focus behind the retina. It can be corrected by a converging lens.
Shortsightedness
This is the opposite of longsightedness in that you can focus on near objects but not on far ones because your eyeball is too long therefore making the light focus before the retina. This can be corrected by using a diverging lens
Colour blindness
Colour blindness is when your cones don't function properly. This cannot be corrected.