Download Biology iGCSE summary notes and more Study notes Biology in PDF only on Docsity!
Plant nutrition
Structure of a leaf Acts
Structure Description
Cuticle A thin, waxy layer that covers the leaf. It reduces water loss by
evaporation and acts as a barrier to the entry of disease.
Upper
epidermis
Few chloroplasts, Transparent to allow light to pass through to the palisade mesophyll
Palisade
mesophyll
A tissue of long, narrow cells. It is the main site of photosynthesis and is close to the source of light
Spongy
mesophyll
A tissue of rounded , loosely packed cells, with spaces in between them. They photosynthesise but not as much as the palisade mesophyll. They form the main gas exchange surface of the leaf , absorbing CO 2 and water vapour.
Xylem A tissue with vessels that supply the leaf with water and
mineral ions in a continuous transport system from the roots.
Phl
oem
Carries the products of photosynthesis to supply the parts of the leaf that cannot photosynthesise with energy
Sto Pores in the lower epidermis of the leaf that allow CO^2 to enter
mata the leaf and oxygen and water vapour to leave.
Guard
cells
Highly specialised cells that can change their shape to open or close the stoma What is Photosynthesis? Photosynthesis is the process of transforming light energy into chemical energy. This is used by green plants and certain other organisms to produce energy. During the process, light energy is captured by chlorophyll and used to convert water and carbon dioxide into glucose which plants can use to store energy. The reaction for photosynthesis is as follows: 6CO2 + 6H2O → C6H12O6 + 6O2 (or) Water + Carbon Dioxide → Glucose + Oxygen. The product of this reaction, glucose is used for energy which can be stored in the plant over the winter, when the plant loses its leaves and therefore cannot photosynthesis. However, the oxygen is released through the stomata as a by-product. Green plants make the carbohydrate glucose from the raw materials carbon dioxide and water At the same time oxygen is made and released as a waste product The reaction requires energy which is obtained by the pigment chlorophyll trapping light from the Sun So photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light Limiting Factors of Photosynthesis If a plant is given unlimited sunlight, carbon dioxide and water and is at a warm temperature, the limit on the rate (speed) at which it
At low light intensities, increasing the intensity will initially increase the rate of photosynthesis. At a certain point, increasing the light intensity stops increasing the rate. The rate becomes constant regardless of how much light intensity increases as something else is limiting the rate The factors which could be limiting the rate when the line on the graph is horizontal include temperature not being high enough or not enough carbon dioxide. Carbon dioxide concentration Carbon dioxide is one of the raw materials required for photosynthesis This means the more carbon dioxide that is present, the faster the reaction can occur This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply The factors which could be limiting the rate when the line on the graph is horizontal include temperature not being high enough or not enough light Mineral Nutrition
Plants require certain mineral ions to live which cannot be obtained through photosynthesis. These include Nitrates, Phosphate, Potassium and Magnesium. Plants can find mineral nutrients in their environment and they are absorbed into their roots through active transport. Nitrates are needed to make amino acids, and chlorophyll and a deficiency can cause limited growth. Magnesium is part of chlorophyll molecules and a deficiency can cause yellow leaves as a result of a lack of chloroplasts. Testing a leaf for starch Method: The dependent variable is the presence of starch in the leaf and the control variables are the volume of water, the time that the leaf is submerged in boiling water and the time that the leaf is in the ethanol. Since ethanol is flammable, the Bunsen Burner is replaced with a water bath to eliminate the risk of the ethanol catching fire. In conclusion, the iodine turns blue/black because starch is present is certain areas of the leaf. Testing how photosynthesis changes with light intensity
Bile – Made in the liver and store in the bladder. It is used for emulsification (Breaking down of lipids into smaller droplets which increases surface area allowing for lipids to be broken down by lipase easier) Villi – Small finger like projections that absorb biological molecules (their adaptations: large surface area to volume ratio that makes diffusion occur faster, short diffusion distance, lacteals allow for absorption of lipids and they have a good network of blood capillaries which gives a high concentration gradient – diffusion occurs faster, the cell linings also have microvilli further increasing the surface area) Diffusion – Absorption Egestion – The removal of undigested food waste through the anus Excretion – The removal of metabolic waste (caused due to a chemical reaction in the cells) Enzymes An enzyme is a special type of catalyst that is made by a living organism. We sometimes call them biological catalysts. Enzymes are large proteins. Therefore they are made from a long chain of amino acids. Different arrangements of amino acids make different enzymes. Enzymes have a region called an active site. This is a part of the enzyme which is complementary to the shape of the substrate. If the substrate does not fit then the reaction will not speed up. this allows enzymes to be very specific about which reactions they speed up Lock and Key model- The substrate has to fit perfectly into the active site for the reaction to be catalysed Induced fit model- The active site changes shape slightly as the substrate binds to it. This can be depicted through the word ‘complementary’ Temperature – Until the optimum temperature is reached, as the temperature of the enzyme increases, so does the rate of reaction. This is due to increased kinetic energy causing increased collisions, which in turn results in more enzyme-substrate complexes. However, once the optimum temperature is reached, the rate of reaction decreases rapidly. This is due to the shape of the active site changing making it so that the substrate can no longer bind to it. Soon the enzyme becomes denatured, which means that it cannot bind to the substrate. This change is permanent and cannot be reverted by cooling down the enzyme. pH – The further away the pH is from the optimum pH the lower the rate of reaction is and the closer the pH is, the higher the rate of reaction is. This is due to the same reason as temperature. When the pH is too high or low, it can cause the active site to change shape, making it so that the substrate cannot bind to it. Describe- describe what is happening in the graph Explain- explain why it is happening The optimum pH and optimum temperature differs for different enzymes. Biological Molecules A biological molecule is a molecule found in a living organism Biological Molecules- Carbohydrates, Proteins, Lipids
Carbohydrates Carbohydrates are polymers If the bonds in a polysaccharide break then monosaccharides are released Examples of monosaccharides: Glucose, Fructose Examples of disaccharides: Sucrose, Lactose Examples of polysaccharides: Starch Carbohydrates contain Carbon, Hydrogen and Oxygen Carbohydrates are broken down in the mouth and the small intestine Broken down by carbohydrases. E.g. Maltase, Amylase Carbohydrates are used as an energy source for chemical reactions Proteins A protein is a polymer made up of a long chain of amino acids (the monomer of proteins) bonded together Proteins contain Carbon, Hydrogen, Oxygen and Nitrogen Broken down by proteases. E.g. Pepsin, Trypsin, Peptidases Broken down in stomach and small intestine Protein is important for growth and producing new cells Lipids Lipids are monomers Lipids contain Carbon, Hydrogen and Oxygen Lipids contain fatty acids and glycogen Lipids are broken down in the small intestine Lipids are broken down by Lipases Lipids are used for insulation and to provide energy for chemical reactions
If you do not consume enough of a particular one of these then it could lead to a deficiency disease such as scurvy. If you consume too much of these it could lead to obesity Carbohydrates are our main source of energy however lipids are another source, if necessary, proteins can be broken down for energy The more active you are, the more energy you need Your age can also determine how much energy you need. If you are a teenager, you might need more energy because you are growing than a person of old age If you are pregnant you would also need more energy as the baby requires a lot of energy
Cell structure
Organell
e
Function
Nucleus The nucleus is the largest organelle. It controls the activities of the cell. It contains chromosomes which carry the genetic material, or genes. Genes control the activity in the cell by deciding which proteins to make. Cell Membrane The cell membrane is a thin layer, like skin, on the surface of cells. It forms a boundary between the cytoplasm and the outside. However, it is not a complete barrier and some chemicals can enter and others leave the cell. This is if the membrane is partially permeable. The membrane can go further and control the movement of some chemicals. This is selectively permeable. Cytoplasm The cytoplasm is the living material that makes up the cell. It has a jelly-like texture.
Ribosomes Ribosomes are the site of protein synthesis Mitochond rion Mitochondria are found in every living cell. Cells that require lots of energy such as muscles and nerves have lots of mitochondria. They carry out some of the reactions needed for respiration, releasing energy that the cell can use. Mitochondria release most of the energy from respiration. Chloroplas t Cells of the green part of plants, especially leaves, contain chloroplasts. Chloroplast's absorb light energy to make food in the process of photosynthesis. They contain a green pigment called chlorophyll. Cells from the part of plants that is not green, such as the flowers, roots and woody stems, do not contain chloroplasts. Vacuole Mature plant cells often have a vacuole, a large central space surrounded by a membrane. This vacuole is a permanent feature of the cell. It is filled up with cell sap, which is a store of dissolved sugars, mineral ions and other solutes. Cell wall The cell wall is a layer on non-living material outside the cell membrane of plant cells. It is one of the reasons why the body of a plant has a fixed shape. Plants cells also absorb water, producing an internal pressure the pushes against adjacent cells, giving the plant support. Without a cell wall strong enough to resist these pressures, this method of support would not be possible. The cell wall is porous so it is not a barrier to water or dissolved substances. This is called freely permeable. Animal cells The main features of animals: o They are multicellular o Their cells contain a nucleus with a distinct membrane o Their cells do not have cellulose cell walls o Their cells do not contain chloroplasts (so they are unable to carry out photosynthesis ) o They feed on organic substances made by other living things o They often store carbohydrates as glycogen o They usually have nervous coordination o They are able to move from place to place
apparatus available. but you can always comment on how accuracy could be improved. Anomaly- An anomalous result is a result that doesn't fit in with the pattern of the other results. Precision- This relates to the smallest division on the scale of the measuring instrument you are using.. Reliability- This is a measure of how similar the results are, if you carried out the same experiment several times. Reliability can be increased by taking multiple results, identifying anomalous results and calculating a mean. A control is not a control variable. It is used to compare to the independent variable. CORMS C- Change - (independent variable) state how many variations you will use O - Organism – E.g. – use same sex, health, age, weight (use the word same) R - Repeat - M - Measure S - Same There are two marks for measure and same
