Biology Unit 2

  • Created by: angel-234
  • Created on: 14-09-15 18:11

B2 1.1- Cells, tissues and organs

  • Human & animals cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant and algal cells contain all the structures seen in animal cells as well as a cell wall. Some also contain chloroplasts and a permanent vacuole filled with sap.
  • A bacterial cell consists of cytoplasm and a membrane surrounded by a cell wall. The genes are not in a distinct nucleus. Yeast is a single-celled organism. Each cell has a nucleus, cytoplasm and a membrane surrounded by a cell wall.
  • Cells may be specialised to carry out a particular function. E.g fat cells, cone cells, root hair cells and sperm cells.
  • Fat cells: small amount of cytoplasm and large amounts of fat, few mitochondria as the cell needs very little energy and they can expand up to 1000x its original size. 
  • Dissolved substances and gases like oxygen move in and out of cells by diffusion.Diffusion is the net movement of particles from an area at a high concentration to an area of lower concentration. The greater the difference in concentration, the faster the rate of diffusion.
  • A tissue is a group of cells with similar structure and function. Organs are made of tissues, one organ may contain several types of tissues.
  • Organ systems are groups of the organ that perform a particular function, the digestive system in a mammal is an example where substances are exchanged with the environment. 
  • Plant organs include stems, roots and leaves. Xylem: transports water & minerals. Phloem: transports dissolved food. Mesophyll tissue: where photosynthesis takes place. 
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B2 2.1- Organisms in the environment

  • Photosynthesis: carbon dioxide + water (+light energy)→ glucose +oxygen. During photosynthesis light energy is absorbed by chlorophyll in the chloroplast of the green parts of the plant, the used to convert carbon dioxide+ water into sugar ( glucose). By- product is Oxygen.
  • Leaves are well adapted to allow the maximum amount of photosynthesis to take place.
  • The rate of photosynthesis may be limited by the shortage of light, low temperature and shortage of carbon dioxide.
  • We can manipulate the levels of light, temperature and carbon dioxide artificially to increase the rate of photosynthesis in food crops. 
  • Plant & algal cells use soluble glucose produced during photosynthesis by: respiration, to convert into insoluble starch for storage. to make fats or oils for storage and to produce fats. proteins or cellulose for use in cells or cell walls.
  • They need other materials including nitrate ions to make the amino acids which make up the proteins.
  • Physical factors affecting the distribution of living organisms include: temperature, nutrients, amount of light, availability of water, oxygen and carbon dioxide. 
  • You can get quantitative data on the distribution of organisms in the environment using: random sampling with quadrats or sampling along a transect. You can determine the range, median, mode and mean using your data.
  • Validity and reproducibility must be considered carefully as it is difficult to control variables in fieldwork, sample size is an important factor in both reproducibility and validity of data. 
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B2 3.1- Enzymes

  • Protein molecules are made up of long chains of amino acids. Proteins act as structural components of tissues, hormones, antibodies and catalysts.
  • Catalysts increase the rate of chemical reactions without changing themselves, enzymes are biological catalysts.
  • Enzymes are proteins, the amino acid chains are folded to form the active site. Substrate (reactant) of reaction fits into the active site of the enzyme.
  • Enzymes activity is affected by high temperature and PH. High temperatures and wrong PH can affect the shape of the active site of an enzyme and stop it working, the enzyme has denatured (active site shape can no longer work anymore.)
  • Digestive enzymes are produced by specialised cells in glands and lining of the gut, they work outside of the body cells and in the gut itself. 
  • Different enzymes catalyse the breakdown of carbohydrates, proteins and fats into smaller, soluble molecules during digestion.
  • Carbohydrate → sugar (made in salivary glands, pancreas and small intestine. Amylase is the catalyst)
  • Proteins → amino acids (made in the stomach, pancreas and small intestine. Protease is the catalyst.)
  • Fats → fatty acids & glycerol (made in the pancreas and small intestine. Lipase is the catalyst.)
  • Enzymes of the stomach work best in acid conditions. Enzymes of the pancreas & small intestine they work best in alkaline conditions.
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B2 3.1- Enzymes

  • Bile is an alkaline liquid produced in the liver to neutralise acids and emulsify fats (break down bug fat droplets to smaller droplets).
  • A layer of mucus in stomach stops it being digested by acid and enzymes.
  • Some microorganisms produce enzymes that pass out of cells and can be used in different ways.
  • Biological detergents contain proteases and lipases.
  • Proteases → to pre-digest protein in baby food making it easier for the baby to get the required amino acids from food.
  • Isomerase → turns glucose to fructose syrup (sweeter than normal glucose so smaller amounts are required)
  • Carbohydrases → turning starch to glucose syrup (a cheap source of providing sweetness for good manufacturers)
  • Enzymes in detergents help to break down biological stains like sweat. They work at lower temperatures so use less electricity, which is cheaper and environmentally friendly. Originally cause allergy problems but this has now been solved, the lower- temperature washes are less good at killing pathogens, but higher temperature can denature enzymes.
  • Enzymes can be produced industrially for both to diagnose or treat diseases.
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B2 4.1- Energy from respiration

  • Aerobic respiration: glucose +oxygen → carbon dioxide + water (+ energy). Most reactions take place in the mitochondria.
  • Energy released during respiration is used to build larger molecules from small ones, muscle contraction and maintaining a steady body temperature in mammals and birds.
  • When you use your muscles you need more glucose and oxygen, and producing more carbon dioxide.
  • Body responses to exercise include: an increase in heart rate, breathing rate and in depth of breathing, glycogen stores in the muscle are converted to glucose for cellular respiration, blood flow to muscle increases. These act to increase the supply of glucose and oxygen to the muscle and remove more carbon dioxide.
  • Muscles become fatigued and won't contact efficiently if they work for a long time as a result, anaerobic respiration may take place if not enough oxygen.
  • Anaerobic precipitation: glucose → lactic acid (+ energy). It releases less energy than aerobic respiration. 
  • After exercise, oxygen is still needed to break down the lactic acid which has built up, the amount of oxygen required is "oxygen debt".
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B2 5.1- Simple Inheritance in animals and plants

  • In body cells, chromosomes are found in pairs. Body cells divide by mitosis to produce more identical cells for growth, repair, replacement or even asexual reproduction. Most types of animal cells differentiate at an early stage of development, plant cells can differentiate throughout their whole life.
  • Cells in the reproductive organs divide by meiosis to form gametes. Body cells have two sets of chromosomes, gametes have only one set.
  • In meiosis, the genetic material is copied and then the cell divides twice to form four gametes, each with a single set of chromosomes.
  • Sexual reproduction gives a rise to variety because the genetic material from two parents is combined.
  • Embryonic stem cells (human embryos) and adult stem cells (adult bone marrow) can be made to differentiate into many different types of cell. Stem cells have the potential to treat previously incurable conditions, we may grow new organs or nerve cells.
  • Gregor Mendel was the first person to suggest separately inherited factors, known as genes. Chromosomes are made up of large molecules of DNA. A gene is a small section of DNA that codes for a particular combination of amino acids, which make a specific protein. Everyone except identical twins has a unique DNA, which can be identified through DNA fingerprinting. 
  • Human body sex chromosomes determine if you are female (**) or male (XY). Some features are controlled by single genes. Different forms of a gene is an allele, some alleles are recessive whilst others are dominant. We can construct genetic diagrams to predict characteristics. 
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B2 5.1- Simple Inheritance in animals and plants

  • Some disorders are inherited.
  • Polydactyly is caused by a dominant allele of a gene and can be inherited from only one parent.
  • Cystic fibrosis is caused by a recessive allele of a gene and so must be inherited from both parents.
  • You can use genetic diagrams to predict how genetic disorders might be inherited.
  • You can use genetic diagrams to predict inheritance of genetic diseases.
  • It is important that people make informed judgements about the use of embryonic stem cells in medical treatment and research.
  • There are a number of economical, social and ethical issues surrounding screening of embryos. 
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B2 6.1- Old & New Species

  • Fossils are the remains of organisms from many years ago that are found in rocks. Fossils may be formed in different ways. Fossils give us information about organisms that lived millions of years ago.
  • Its is very difficult for scientists to know exactly how life on Earth began because there is little evidence that is valid. 
  • We can learn from fossils how much or how little organisms have changed as life has developed on Earth.
  • Extinction may be caused by new predators, new diseases or new, more successful competitors.
  • Extinction can be caused by environmental change over geological time.
  • Mass extinctions may be caused by single catastrophic events such as volcanoes or asteroid strikes.
  • New species arise when two populations become isolated.
  • Populations become isolated when they separated geographically e.g. on islands
  • There are natural cycles linked to environmental change when species from and when species die out.
  • In an isolated population, alleles are selected that increase successful breeding in the new environment.
  • Speciation takes place when an isolated population becomes so different from the original population that successful interbreeding can no long take place.
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