Calderglen High School Department Cell Course Notes 1
Cells All living organisms are made-up of cells. The detailed structure of these cells is too small to be seen with the naked eye. Biologists use a microscope to view cells An animal cell Image BBC Bitesize cell membrane nucleus cytoplasm ribosome mitochondrion A Plant cell Image BBC Bitesize cellulose cell wall cytoplasm chloroplast nucleus cell membrane vacuole ribosome mitochondrion NB ribosomes and mitochondria are not visible using a light microscope. 2
The following table contains information about the functions of the parts animal and plant cells. Name of structure nucleus cell membrane cytoplasm ribosomes mitochondria Structure found in an animal or plant cell These structures are found in both animal and plant cells Function Contains genetic information that controls most cell activities. Controls what enters and leaves the cell. The membrane is selectively permeable. All the chemical reactions of the cell occur in the cytoplasm. The reactions are controlled by enzymes. Ribosomes are where proteins are made. Enzymes are made of proteins and growing cells would have many ribosomes in the cytoplasm They are found in the cytoplasm where aerobic respiration takes place to release energy from food. cellulose cell wall chloroplasts These structures are found in plant cells only This strengthens the cell wall and provides support. They contain chlorophyll which absorbs light energy for photosynthesis. vacuole The permanent vacuole, contains a solution of minerals, sugars and amino acids, provides support. 3
Fungus structure cell membrane nucleus cytoplasm fungi cell wall ribosome mitochondrion Fungi have a very similar structure to plant and animal cells. They contain cytoplasm, a cell membrane, a nucleus ribosomes and mitochondria. However the cell wall has a different structure from plant cells. Chloroplasts are not found in fungi, this means they do not carry out photosynthesis and are unable to make their own food. Fungi feed on other organisms to obtain their energy source. Bacteria Bacterial cells are much simpler then animal or plant cells. cytoplasm bacterial cell wall chromosome ribosome cell membrane plasmid Bacteria are much simpler cells than either plan or animal cells. They have a cell wall which is made of different material and has a different cell structure from plant cells. The genetic material is contained in the chromosome which is a large ring of DNA. Bacterial cells also contain plasmids which is a small ring of DNA. Ribosomes are found in the cytoplasm of the cell and bacterial proteins are made on these structures. Respiration, the breakdown of food in living cells to release energy, occurs in the cytoplasm of the cell as bacteria do not contain any mitochondria. 4
Cell membrane The cell membrane forms the outer boundary of a cell and it is made of lipids and proteins. The structure of the cell membrane is shown below. Protein molecules Protein molecule Double phospholipid layer Phospholipid molecule Channel or pore The cell membrane is selectively permeable which means that only certain substances can pass through from one side of the membrane to the other. Transport across the membrane can be passive and active. Passive transport means that the movement of substances does not require energy to occur however active transport of materials across the membrane does require energy. Investigating Diffusion Substances such as oxygen, dissolved food e.g. glucose molecules are continually diffusing into cells and carbon dioxide molecules are continually diffusing out of cell. high concentration Diffusion is the movement of molecules down a concentration gradient from a higher to a lower concentration. lower concentration 5
Diffusion is the movement of molecules from an area of high concentration to an area of lower concentration. Diffusion is an example of passive transport because it does not require energy. The importance of diffusion to a living cell Living cells rely on diffusion to provide them with the substances they need to live and grow, and to rid them of waste substances. Diffusion of substances occurs in every living cell. Some substances diffuse into the cell while others diffuse out. Cell membranes are very thin to allow some materials to diffuse through them easily. Materials such as oxygen, amino acids and glucose enter the cells by diffusion. This is because the concentration of oxygen, amino acids and glucose inside the cell is lower than the surrounding blood so these substances move into the cell. Living cells produce carbon dioxide and the level inside the cell increases to a level higher than the surrounding blood, so carbon dioxide diffuses out of the cell. The diagram below is of a typical animal cell. The arrows indicate the direction of movement oxygen and dissolved food in to the cell. Carbon dioxide and waste materials diffuse of the cell. cell membrane nucleus oxygen glucose carbon dioxide cytoplasm amino acids Visking membrane is just like a cell membrane because the size of the pores in the visking membrane gives it similar permeability to that of a real cell membrane. 6
Osmosis a special type of diffusion This experiment demonstrates the diffusion of water, through a selectively permeable membrane. This is called osmosis and is a passive process. Osmosis involves the movement of water from a region of high water concentration to a region of lower water concentration through a selectively permeable membrane. Osmosis and Living Cells When plant or animal cells are bathed in solutions of different concentrations to the cell contents, changes in the cells occur. Osmosis and Animal Cells The outer boundary of an animal cell is the cell membrane. If water enters an animal cell by osmosis it swells up and eventually burst. If animal cells lose water by osmosis they shrivel up and the cell membrane becomes crinkled. Membrane of the red blood cell Pure water Red blood cell in a 5% salt solution Red blood cell in pure water swell up and burst. Red blood cell in a 5% salt solution shrink. Image BBC Bitesize 7
Plant cells and osmosis Plant cells have a strong wall outside the membrane. If a plant cell loses water by osmosis it keeps its shape however the membrane detaches from the cell wall and the vacuole becomes smaller. The cell is plasmolysed. Plant cells that gain water by osmosis swell up and become firm. The cell is turgid. Plant cells and osmosis cell wall cytoplasm vacuole nucleus cell membrane Cell bathed in a 10% salt solution Cell bathed in pure water A plant cell in 10% salt Active water. transport It is plasmolysed A plant cell in pure water swells up. It is turgid. Active Transport Active transport is the movement of particles across a cell membrane. In active transport, particles move from a lower to a higher concentration. The particles move against the concentration gradient and therefore energy is required for this process to occur. There are proteins in the cell membrane 8
known as carrier proteins which pick up the particles and take them through the cell membrane against the concentration gradient. Active transport Low concentration of particles on one side of the membrane. + + + + + + + + + + + + + double phospholipid layer Carrier protein in the cell membrane High concentration of particles on this side of the membrane. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + = particles 9
Investigating Cell division Chromosomes are found in the nucleus of the cell and carry coded instructions called genes from one generation of cell to the next. When most plant and animal cells divide, their nuclei pass through the same series of changes, called mitosis. A cell chromosomes nucleus chromatid A chromosome centromere Image BBC Bitesize Cell division is important as it allows organisms to grow and repair damaged parts e.g. cuts and broken bones. Cell division is a means of increasing the number of cells in an organism. The cell simply divides into two identical cells. Keeping the chromosome number correct Each species of plant and animal has a characteristic number of chromosomes in the nucleus of each of its body cells which is always the same for the specific species. For example, the body cells of human beings contain 46 chromosomes. It is essential that each cell formed as a result of mitosis receives a full complement of chromosomes. This is necessary because the chromosomes contain the genetic code of the particular species. As the cells of a multicellular organism grow and develop, the genetic code will provide the animal or plant with all the characteristics of its species. 10
Summary of the stages of cell division The diagram below represents stages in the process of mitosis in the correct sequence. After a period of growth, mitosis starts again each cell Chromosomes become visible in the nucleus. Two identical daughter cells have been produced. Chromosomes shorten and appear as chromatids joined at the centromere Spindle fibres pull chromatids to opposite ends of the cell. Nuclear membrane disappears and the chromosomes line up along the equator of the cell. 11
Core Notes Cancer is a condition where cells in a specific part of the body grow and reproduce uncontrollably. The cancerous cells can invade and destroy surrounding healthy tissue, including organs. Properties and uses of microorganisms Microorganisms can be used in industry to make products useful for humans. They grow rapidly and can use a diverse range of food sources. Yeast is a single celled fungus that can be used in the brewing industry to make alcohol and also can also be used in the baking industry to make bread rise. Bacteria can be used to make yoghurt and can also be used to breakdown sewage. 12
DNA and Protein Synthesis Deoxyribonucleic Acid (DNA) is a chemical molecule that carries genetic information. DNA is found in plant, animal, bacterial and fungal cells. In plant and animal cells it is located in the nucleus DNA is made of subunits Diagram of a DNA subunit base There are four different bases A (adenine), T (thymine), G (guanine) and C (cytosine) Chain of subunits joined together DNA backbone DNA uncoiling bases centromere Genes on the chromosome 4 bases present in DNA Image BBC Bitesize Base Pairing adenine (A) always pairs with thymine (T) cytosine (C) always pairs with guanine (G) 13
DNA double helix Image BBC Bitesize A molecule of DNA consists of two strands of DNA called a DNA doublestranded helix. The double helix looks like a ladder that has been twisted into a spiral. In the nucleus DNA is arranged into chromosomes. Each chromosome is made up of hundreds of genes, each coding for a different protein. Protein Synthesis Proteins are made of amino acids. The structure and function of a protein is determined by the number and type of amino acids present. The base sequence on a DNA molecule determines amino acid sequence in a protein. A gene is a section of DNA which codes for a protein. How does the information on the DNA in the Nucleus get to the ribosomes in the cytoplasm? DNA molecules are found in the nucleus of the cell. Ribosomes are organelles that assemble proteins and are found in the cytoplasm. DNA is too large to move out of the nucleus, so a section is copied into a molecule called messenger RNA (mrna). mrna carries a complementary copy of the code of DNA, in the nucleus to a ribosome where the protein is assembled. Proteins are complex molecules made of a chain of amino acids. Image BBC Bitesize Protein 14
Each protein is made from a precise sequence of amino acids. They perform many structural and functional roles in all living systems. Structural Antibodies Enzymes Hormones Receptors Function Example of protein Support Fight against invading viruses Biological catalysts Chemical messengers Proteins that are sensitive to other molecules Enzymes Properties of Enzymes Enzymes are made of protein and are produced by all living cells. They are biological catalysts which increase the rate of a chemical reaction. Enzymes are reusable as they are unchanged by the chemical reaction. Enzymes act upon a specific substrate to produce a product. Each enzyme has a particular shaped area on its surface called the active site. The shape of the active site of an enzyme is complementary to its specific substrate. Complementary shapes Active site Enzyme molecule site Substrate molecule site 15
Enzymes can be involved in degradation and synthesis reactions. Synthesis enzyme - Build-Up Reaction Image BBC Bitesize In this reaction, the enzyme brings about the building up (synthesis) of a large complex molecule from simple substrates. 16
Degradation enzyme- Breakdown reaction Image BBC Bitesize In this reaction, the enzyme promotes the breakdown of a complex substrate into small, simpler products. Factors Affecting Enzyme Activity To function efficiently an enzyme requires a suitable temperature and a suitable ph. Effect of Temperature Optimum temperature 40 o C Enzyme denatured Image BBC Bitesize At very low temperature (0 o C) enzyme molecules are inactive but undamaged. As temperature increases the rate of the reaction increases as enzymes can combine with substrate molecules faster. A temperature is reached called the optimum temperature. This is the temperature at which the enzyme is most active and the rate of the reaction is at its fastest. 17
When the temperature increases above the optimum the shape of the active site is changed and the enzyme can no longer bind to its substrate. The rate of reaction therefore decreases. At 50 o C the enzyme s shape is completely changed and it is permanently damaged so will never bind to its substrate again. The enzyme is said to be denatured and the reaction rate is zero. substrate enzyme denatured enzyme Effect of ph ph is used to measure acidity or alkalinity of a solution Each enzyme is most active at a particular ph. This is called the optimum ph. Optimum for enzyme 1 (ph 2.5) Optimum for enzyme 2 (ph 7) Optimum for enzyme 3(pH 9) ph If an enzyme (except pepsin) is exposed to an extremely low ph (acid) it loses its important shape, the active site can no longer combine with substrate and the enzyme will be DENATURED. Image BBC Bitesize Each enzyme is most active in it s optimum conditions. 18
Genetic Engineering Genetic information can be tranferred from one cell to another (delete) naturally or by genetic engineering. Stages of Genetic Engineering chromosome extracted and required gene identified plasmid extracted from (delete vector) bacterial cell gene cut out from chromosome using enzymes plasmid cut open using enzymes gene sealed into plasmid using enzymes altered plasmid inserted into host bacterial cell. Modified bacterial cells increase in number 19
Core Notes Uses of Genetic Engineering Insulin - Human insulin produced by Genetic Engineering which can be given to people who do not make enough insulin naturally and would therefore suffer from Diabetes (and may even die) This genetically modified (GM) organism can now produce the required product. Human Growth Hormone- Given by regular injection to children who do not make enough of their own. Growth Hormone prevents reduced growth and Dwarfism Biological Detergents- They contain enzymes produced by genetic engineering. They remove stains at lower temperatures and are therefore energy efficient. Controversial Biological Procedures:Stem Cells Stem cells are found in all plants and animals. They are produced by cell division and can specialise into a range of different cell types. Stem cells can be used in technology to grow many different types of cells and scientists are investigating the possible uses of these cells in the treatment of disease. In the future, stem cells could be injected into broken bones in order to speed up healing or used to help repair damage the heart suffers after a heart attack. 20
Photosynthesis Photosynthesis is the process in green plants involving the manufacture of glucose sugar from carbon dioxide gas and water, producing oxygen gas as a by-product. Leaves contain a special pigment known as chlorophyll that allows plants to capture the energy of light to drive the process. The sugar can be used by the plant cells themselves during respiration, stored in the leaves as starch or built up into cellulose, a chemical that makes up cell walls. Summary: Carbon dioxide + Water light energy Chlorophyll Sugar + Oxygen Leaf structure cuticle Image BBC Bitesize 21
(Delete) Photosynthesis The process of photosynthesis takes place in the chloroplast and occurs in two stages: the light reactions and the carbon fixation stage. Stage 1 The light reaction The light energy from the sun is trapped by chlorophyll in the chloroplasts and is converted into chemical energy in the form of ATP. Water is split to produce hydrogen and oxygen. Excess oxygen diffuses from the cell. Sunlight energy is absorbed by the chlorophyll and converted to chemical energy. Chemical energy is used to split water (H2O) Chemical energy is used to make ATP Oxygen (diffuses out of the leaf) Hydrogen (attaches to a hydrogen acceptor) This forms ATP (energy for the cell) Hydrogen and ATP are needed for the next stage in photosynthesis. Excess oxygen is a by product and diffuses out of the cell. 22
Stage 2 Carbon Fixation Hydrogen and ATP produced by the light reaction is used with carbon dioxide to produce glucose in an enzyme controlled process. hydrogen acceptor hydrogen Carbon fixation stage ATP Hydrogen acceptor will return to the light stage and pickup more hydrogen. Carbon dioxide Sugar The sugar produced in the carbon fixation stage can be used: As an energy source for respiration Converted to starch (storage carbohydrate) Converted to cellulose (structural carbohydrate that makes up the cell wall) 23
Apparatus to measure the rate of photosynthesis by production of oxygen: Lamp to provide light for photosynthesis Measuring cylinder to collect and measure the volume of gas produced Oxygen bubbles Image BBC Bitesize Aquatic plant e.g. Elodea in a sodium bicarbonate solution The apparatus is set up as shown above and left for 10 minutes to adjust to the environmental conditions. The rate of photosynthesis is measured by counting the number of bubbles of oxygen per minute. Limiting Factors in Photosynthesis If a certain factor is in short supply (limited availability) it will reduce the rate of photosynthesis this is called a limiting factor. Examples of limiting factors are: Concentration (availability) of carbon dioxide Light intensity Temperature 24
Limiting Factors Graph The graph below shows the effect of increasing carbon dioxide concentration on the rate of photosynthesis at different light intensities and temperatures. Limiting factors graph 0.5 D C Light intensity 20 kilolux Temperature 16 o C Rate of photosynthesis (cm 3 CO2 used per minute) 0.4 0.3 0.2 0.1 A B Light intensity 20 kilolux Temperature 10 o C Light intensity 10 kilolux Temperature 10 o C 0 5 1 0 1 5 2 0 2 5 Carbon dioxide concentration (%) Area of graph being limited A Limiting factor Carbon dioxide concentration. Explanation As the concentration of carbon dioxide increases to 1% the rate of photosynthesis increases. B Light intensity By comparing points B and C on the graph- the only difference between these to points is light intensity. Point B has a lower light intensity therefore the rate of photosynthesis is lower. C Temperature By comparing points C and D on the graph- the only difference between these to points is temperature. Point C has a lower temperature therefore the rate of photosynthesis is lower. 25
The purpose and importance of respiration Respiration The chemical energy stored in glucose is released by all living cells through a series of enzyme controlled reactions called respiration. The energy released from the breakdown of glucose is used to generate ATP (adenosine triphosphate). ATP is an important substance that is found in all living cells. Structure of ATP Adenosine Pi Pi Pi Pi = inorganic phosphate High energy bond ATP is formed using the energy released by the respiration of glucose. It is a high energy molecule. ATP Formation and Breakdown ATP plus chemical energy from breakdown of glucose Chemical energy is released ADP + Pi ATP is formed (delete when ADP (adenosine diphosphate) and an inorganic phosphate are joined) using energy from the respiration of glucose. When ATP breaks down, energy is released (delete along with ADP and inorganic phosphate). This energy released can be used for cellular activities including muscle contraction, cell division, protein synthesis and transmission of nerve impulses. 26
Aerobic respiration If oxygen is available to the cells the type of respiration that takes place is known as aerobic respiration. The oxygen for aerobic respiration is obtained by breathing in air from the surroundings (air contains oxygen). The breakdown of glucose consists of many reactions which are controlled by enzymes. glucose molecule This stage takes place in the cytoplasm. The chemical reactions do not need oxygen to occur 2 ATP molecules are produced at this stage Aerobic stageoxygen is required for this stage to occur This stage takes place in the mitochondria pyruvate A large amount of ATP molecules are produced Carbon dioxide and water Large amount of ATP produced Word Equation Summary for Aerobic Respiration 27
Glucose + oxygen Carbon dioxide + Water + 38 ATP molecules Fermentation Fermentation takes place in the absence of oxygen. This occurs in the cytoplasm of animal or plant cells. Fermentation in Animal Cells This could be due to an animal living in an environment that has a low level of oxygen e.g. mud or stagnant water. However another reason for the short supply of oxygen could be due to an animal exercising vigorously and consequently it is unable to breathe in fast enough to get sufficient oxygen to the respiring cells. Under fermentation conditions, glucose can only be partly broken down. The chemistry of fermentation in animal cells Glucose molecule This stage takes place in the cytoplasm of the cell. The chemical reactions do not need oxygen to occur, (fermentation stage) Pyruvate Lactate 2 ATP molecules are formed at this stage NO ATP formed here ie pyruvate lactate During fermentation only 2 ATP molecules are produced from the break down on one glucose molecule. Fermentation in animals does not produce carbon dioxide or water, the end product is lactate. Word Equation Summary for fermentation in Animal Cells Glucose Lactate + 2 ATP molecules 28
Aerobic respiration animals Fermentation in plant and yeast Oxygen required yes no no ATP yield (produced per glucose molecule) Large amount 2 ATP molecules 2ATP molecules Product(s) Carbon dioxide and water Lactate ethanol + carbon dioxide Fermentation in Plants and Yeast Fermentation in plant root cells could be due to roots being surrounded by water logged soil which is low in oxygen. The chemistry of fermentation in plant and yeast cells Glucose molecule This stage takes place in the cytoplasm of the cell The chemical reactions do not need oxygen to occur, (fermentation stage) Pyruvate 2 ATP molecules are formed at this stage NO ATP formed here Ethanol and carbon dioxide During fermentation only 2 ATP molecules are produced from the break down on one glucose molecule. Word Equation Summary for Fermentation in Plant Cells and Yeast Cells 29 Glucose ethanol + carbon dioxide + 2 ATP molecules