B2 Edexcel Notes

This is what I wrote up in the last few weeks before the exam... I haven included the process of cloning becasue I had forgotten and I could remember.. but everything else is there!

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  • Created by: Meghna
  • Created on: 06-11-12 21:18
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Digestion: Food is chewed in the mouth, where the saliva contains amylase enzymes that start to break
down carbohydrates into glucose When the food is broken down small enough, it is swallowed as a bolus and
started to enter the alimentary canal, from the oesophagus. The food is moved down the oesophagus by
actions of relaxing and contracting muscled wall called peristalsis. The food then enters the stomach, to be
broken down my hydrochloric acid and enzymes that can work best in acidic conditions, such as pepsin, a
protease to break down proteins into amino acids. The Liver creates bile that is stored in the gall bladder,
which is released into the small intestine too emulsify fats into smaller droplets and neutralizing it as the fats
are acidic and bile is alkaline. Fats are broken down further by lipase as fatty acids and glycerol. The food
starts to enter the small intestine, where pancreas secretes enzymes to continue the further breakdown of
food. In the small intestine, there a small, finger like structures called villi. These villi have a large surface area
and thin walls to absorb nutrients quickly and efficiently. There is a network of capillaries in each villi so that
diffusion of proteins and sugars can happen easily as there is always a low concentration gradient in the
blood. Villi also have a lacteal, which absorbs ad stores fats. In the large intestine, water is removed by
diffusion and enters the blood stream, whilst the rest left is indigestible waste that passes out through the
rectum and then the anus as faeces.
Plants: Water evaporates from the plants leaves because of transpiration. This causes more water and
dissolved minerals to be pulled up through the xylem to the leaf. Because of this, more water is needed by
the roots to keep this process ongoing. Root hair cells use osmosis to allow water to diffuse across it's
partially permeable membrane from the soil when there is a low concentration of water in the plant than the
soil. However, there are usually more minerals in the plant roots than in the soil, so the absorption of minerals
cannot happen by diffusion. A spate process called active transport takes place where the minerals are taken
in the root hair cells using energy from respiration, as it is being taken in against the concentration gradient.
The Xylem carries water and minerals from the roots to other parts of the plant, whilst the Phloem carries
glucose made from the leave which is converted into sucrose to other parts of the plant.
Leaf adaptations: Plants have broad leaves to maximise the rate of photosynthesis as chlorophyll, a pigment
in the leaves helps with it. They are very thin, so gas exchange can happen quicker. The leaf has a waxy
coating to minimise loss of water by evaporation. The upper epidermis is transparent to allow the sunlight to
enter the palisade cells, which are close to the surface of the leaf, to photosynthesis efficiently, as they
contain chloroplasts that contain chlorophyll. The underside of the plant has stomata which are pores that
allow gas exchange of gases like oxygen and carbon dioxide. They close during the night as the plants do not
photosynthesis then. Veins in the leaf have a constant supply of sucrose and water for the leaves.
Limiting Factors in Photosynthesis: Plants need a certain amount of carbon dioxide, water, light and
temperature in order for the rate of photosynthesis to increase. If the rate of photosynthesis stops increasing
when measuring a certain factor, it means that another factor is responsible for limiting photosynthesis.
Meiosis and Mitosis: Meiosis and mitosis are types of cell divisions. Mitosis happens when a part of the
body has to be repaired, or needs to grow. The parent cell has 2 pairs of chromosomes, s it is a diploid cell. It
replicates the chromosomes so it has four pairs, and then divides itself to create 2 cells that have 2 pairs of
chromosomes in each, and are diploid also. These are called daughter cells and are genetically identical.
However, Meiosis is only used for the production of gamete cells. Like mitosis, it starts of with a diploid cell,
replicates and divides in two. After wards, it divides again to create for cells with only one pair of
chromosome each. This makes a haploid cell and is genetically different as the chromosomes are randomly
distributed.
Microscopes and Bacteria : Light microscopes can magnify cells so that we can see it's small structures
which increases our understanding of how our body works. Light microscopes made it look like bacteria had
no nucleus however electron microscopes showed 2 types of DNA. Bacteria have chromosomal DNA that
contains most of the genetic information and Plasmid DNA that contains some. It also has a cell wall and cell
membrane, and if a flagellum is present, then it helped the bacteria to move around.
Aerobic respiration: Aerobic respiration takes place as red blood cells carry glucose and oxygen to respiring
tissues and convert them to carbon dioxide, water and energy to do daily tasks. Oxygen enters the blood and
carbon dioxide exits our lungs in the alveoli through a concentration gradient. This is easy to do as capillaries
that carry the gases and blood surround the alveoli and are very thin so diffusion of gases can happen easily
and quickly.

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Anaerobic respiration: Anaerobic respiration takes place after increased exercise. Our muscles are working
harder and need more energy at a faster rate to do so, so oxygen and glucose in the blood need to be
pumped faster by the heart so it gets to the respiring tissues. At a point, oxygen will not be able to be
delivered to the muscles fast enough, so anaerobic respiration starts, it makes energy without oxygen.
Glucose is broken down to make lactic acid and energy.…read more

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High blood cholesterol also leads to heart
disease. Plant stanol esters are now produced in spreads.
Genetic Engineering
1. Human insulin gene is cut out from the DNA by restriction enzymes and inserted into the plasmid DNA
of live bacteria. This can improve the health of people who are diabetic by consuming the bacteria in foods.…read more

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DNA discovery: Maurice Wilkins and Rosalind Franklin X-rayed a purified DNA and worked out how the atoms
in the DNA were arranged. Afterwards, Francis crick and James Watson used Rosalind's DNA to make a 3D
Molecular model of how they thought DNA looked .Because the x-ray image was so detailed, they realised it
was a Double helix shape. From 2003, a project called The Human Genome project started, where 18
countries were involved so that scientists can collect data of peoples DNA.…read more

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