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Biology GCSE AQA Unit 2
Transcript of Biology GCSE AQA Unit 2
Cytoplasm - where most of the chemical reactions take place
Cell membrane - controls the passage of substances into and out of the cell
Mitochondria - where most energy is released in respiration
Ribosomes - where protein synthesis occurs.
Cell walls (only in plants) - strengthens the cell
Chloroplasts (only in plant cells) - absorb light energy to make food
A bacterial cell consists of cytoplasm and a membrane surrounded by a cell wall.
Yeast is a single-celled organism and these cells have a nucleus, cytoplasm, and a membrane surrounded by a cell wall.
Cells are usually specialised for their particular function Cells and cell structure Plants and algae use light energy to make their own food. The conditions which plants are grown in can be altered to increase growth.
carbon dioxide + water -> glucose + oxygen
Light energy is absorbed by chlorophyll which can be found in chloroplasts in some plant cells and algae.
The rate of photosynthesis can be altered by changing the following factors:
concentration of carbon dioxide Photosynthesis Evidence for early forms of life comes from fossils. Old and New Species Have Barack Obama being a badass Example:
Red blood cells - they're small which helps them to pass through narrow capillaries. They're in a flattened disc shape which allows rapid diffusion of oxygen. They contain haemoglobin. The haemoglobin absorbs oxygen in the lungs and helps to release oxygen in the rest of the body. To increase space in the blood cell for haemoglobin. Plant Organs Plant organs include stems, roots and leaves. Examples of plant tissues include:
epidermal tissues, which cover the plant
mesophyll, which carries out photosynthesis
xylem and phloem, which transport substances around the plant Organisms and their environment The distribution of living organisms in a particular habitat may be affected by physical factors such as temperature and amount of light. Transects and quadrats are used to find the mean, median and average number of each living organism in specific habitats. Proteins Proteins have lots of different functions whether they're inside the cells of living organisms or outside. Like enzymes, proteins are now widely used. Protein molecules are made up of long chains of amino acids. The chains are folded into a particular shape which allows other molecules to fit into the protein. Proteins act as:
structural components of tissues such as muscles
Cataslysts are an important part of increasing the rate of chemical reactions. Biological catalysts are called enzymes and enzymes are proteins. Enzymes The shape of an enzyme is very important to consider for the enzyme's function. High temperatures can change the shape. Depending on the type of enzyme, they work best at different pH values. The digestive cells, catalyse the breakdown of large molecules into smaller molecules which are easier to digest. Amylase is an enzyme which is produced in the salivary glands, the pancreas and the small intestine. It catalyses the breakdown of starch into sugars in the mouth and small intestine. Protease enzymes are produced by the stomach, pancreas and the small intestine. These enzymes catalyse the breakdown of proteins into amino acids in the stomach and small intestine. Lipase enzymes are produced only in the pancreas and the small intestine. They catalyse the breakdowns of lipids (which are fats and oils) into fatty acids and glycerol in the small intestine. Hydrochloric acid is also produced in the stomach. This is because the enzymes in the stomach work best in acidic conditions. More Enzymes The liver produces bile which is stored in the gall bladder before being released into the small intestine. Bile neutralises the acid which was added to food in the stomach. This then benefits the enzymes in the small intestine because they work best in alkaline conditions. Biological detergents may contain fat-digesting and protein digesting enzymes called lipase and protease. They're also more environmentally friendly because they're more effective at lower temperatures compared to other detergents which uses less energy and reduces the carbon footprint. Proteases are used to pre-digest some of the proteins in baby foods. In order to convert starch into sugar syrup, carbohydrases are used. Isomerase is used to convert glucose syrup into fructose syrup. Fructose syrup is a lot sweeter so small amounts are often used in slimming foods. Aerobic Respiration The chemical reactions inside cells are controlled by enzymes. Aerobic respiration uses oxygen and during this process, chemical reactions happen where energy is released and glucose and oxygen are used. Most of these reactions take place in the mitochondria. Aerobic respiration is always taking place in animals and plants. glucose + oxygen -> carbon dioxide + water ( + energy)
C6H6O6 + O2 -> 6CO2 + 6H2O ( + energy) During exercising, some changes take place where the heart race increases and the rate and depth of breathing increases. These both increase the blood flow and therefore increase the supply of sugar and oxygen and increase the rate of removal of CO2. Anaerobic Respiration During exercise, if the muscles aren't getting enough oxygen, anaerobic respiration takes place to obtain energy. Anaerobic respiration - the incomplete breakdown of glucose. When anaerobic respiration takes place, lactic acid is produced. Much less energy is released then during aerobic respiration because the glucose isn't being broken down properly. A result of this is the lack of oxygen which can only be cured by oxidising the lactic acid to carbon dioxide and water.
When you exercise too much, your muscles become tired and sore because they stop contracting sufficiently. A cause of this is a build up of lactic acid because there isn't enough oxygen reaching the muscles. Blood flowing through the muscles removes the lactic acid. Inheritance Characters are passed on into next generations for plants and animals. Definitions
Homozygous - having identical alleles at corresponding chromosomal loci.
Heterozygous - having dissimilar alleles at corresponding chromosomal loci.
Genotype - The genotype is the combination of alleles for a given gene possessed by an individual organism.
Phenotype - The phenotype is the outward manifestation, or trait, that is a consequence of the genotype. Gregor Mendel Gregor Mendel was an Austrian monk who in the 1860s began to experiment with pea plants. Mendel wanted to understand how living organisms passed on physical characteristics from one generation to the next. Mendel focused on the following traits; height, colour and shape of pea seeds. He cross-pollinated plants to control the plants that he was producing.
When Mendel took seeds from tall plants and matched them up with seeds from other tall plants he predicted that the offspring would be tall, but only some were tall. Mendel discovered that there is a dominant and recessive gene. When reproducing, each parent can pass only one gene to their offspring, from each gene pair. This means that the offspring will inherit one gene from each parent, making a new gene pair. Cell Division Inside body cells there are chromosomes which are usually in pairs. Body cells divide by 'Mitosis'. Mitosis - A type of cell division that results in two daughter cells each the same as the parent nucleus. The chromosomes contain genetic information. Body cells have two sets of chromosomes. Gametes are formed when reproductive cells from the reproductive organs (for humans, testes and ovaries) divide. This is 'Meiosis'. Meiosis - A type of cell division that results in two daughter cells each with half the chromosome number of the parent cell. Gametes only have one set of chromosomes. Stem Cells Cells from human embryos and adult bone marrow are called 'stem cells'. These cells can be made to resemble and function any type of cell. They can develop into any type of cell! Treatment with stem cells could develop and help conditions such as paralysis. Genetic Variation The chance of variation increases in sexual reproduction because an allele comes from each parent. A gene is a small section of DNA.
Each gene codes for a specific combination of amino acids which make up a specific protein.
Some characteristics are controlled by a gene. Each gene may have different forms called alleles.
An allele that controls the development of a characteristic when it is present on only one of the chromosomes is a dominant allele.
An allele that controls the development of characteristics only if the dominant allele is not present is a recessive allele.
Chromosomes are made up of large molecules of DNA which has a double helix structure. Genetic Disorders Some disorders are inherited. Polydactyly is where you are born with extra toes or fingers and it's caused by a dominant allele of a gane and can therefore be passed on by one parent only who has the disorder. Cystic fibrosis is a disorder of the cell membranes whic must be inherited from both parents. The parents may be carrying the disorder without actually having it because the disease is caused by the recessive gene and therefore can be passed on by parents whom don't have the disorder themselves. Fossils are the remains of organisms from many years ago which can be found in rocks. Fossils can be formed in a few different ways:
from the hard parts of animals that don't easily decay
when parts of the organisms are replaced by other materials while the organism decays
preserved traces of organisms e.g prints
from organisms which couldn't decay due to conditions that weren't sufficient for decomposition to take place
A lot of early forms of life were soft-bodied and therefore, there aren't fossils from these organisms because the bodies decomposed. The small amount of traces that were still left have been mostly destroyed by geological activity.
Causes for extinction are:
through the cyclical nature of speciation
changes to the environment over geological time
new, more successful competitors
a single catastrophic event, e.g asteroid etc