Structure and functions in living organisms

• Organelles -> cells -> tissues -> organs -> organ systems -> organism
• Organelle: a sub-cellular specialised unit which performs a specific function.
• Cell: The basic building block of all living organisms. The smallest unit that can live on its own and that makes up all living organisms and the tissues of the body.
• Tissues: A group of cells working together to perform a shared function (often with similar structures).
• Organs: A structure made up of groups of different tissues, working together to perform specific functions.
• Organ system: A group of organs with related functions, working together to perform certain functions within the body.
• Nucleus: Contains genetic material, including DNA, which controls the cell’s activities
• Cytoplasm: A jelly-like material that contains dissolved nutrients and salts and structures called organelles. It is where many of the chemical reactions happen.
• Cell membrane: Its structure is permeable to some substances but not to others. It therefore controls the movement of substances in and out of the cell. (Semi-permeable membrane)
• Cell wall: Made from cellulose fibres and strengthens the cell and supports the plant.
• Mitochondria: Organelles that contain the enzymes for respiration, and where most energy is released in respration.
• Chloroplasts: Organelles that contains the green pigment, chlorophyll, which absorbs light energy for photosynthesis. Contains the enzymes needed for photosynthesis.
• Ribosomes: A tiny organelle where protein synthesis occurs.
• Permanent vacuole: Filled with cell sap to help keep the cell turgid.
• Plant cells have a cell wall in addition to a cell membrane, whereas animal cells only have a cell membrane. Plants use cell walls to provide structure to the plant. Plant cells contain organelles called chloroplasts, while animal cells do not. Chloroplasts allow plants to make the food they need to live using photosynthesis, but animals acquire glucose from their diet.
• Cell differentiation is the process by which a cell changes to become specialised for its function. Differentiated cells lose the ability to make new copies of themselves, so multicellular organisms must retain some unspecialised cells that can replenish cells when needed. (These unspecialised cells are called stem cells).
• Stem cell advantages: Stem cell research can be used to treat a wide variety of diseases and injuries, such as diabetes or nerve paralysis - saving more lives in the long run; Stem cell research can be used to aid the discovery of treatments (eg: cancers); Stem cells can be used to replace damaged cells, regenerate tissues, and even cure certain medical conditions (diabetes, Parkinson’s disease, heart disease).
• Stem cell disadvantages: Stem cells have a risk of being rejected by the body’s immune system; Stem cells have a risk of turning into cancer cells; If the sample of stem cells is contaminated by a virus, they could be transmitted to the patient; Ethical problems - There is a destruction of embryos produced from fertilisation. Some believe that life starts after fertilisation, so it is essentially “killing”.
• There are two different types of stem cells: embryonic stem cells and adult stem cells. Embryonic stem cells are pluripotent, meaning they have the ability to develop into any type of cell in the body. Adult stem cells are multipotent, meaning they can only develop into certain types of cells.
• In carbohydrates, the chemical elements present are carbon, hydrogen and oxygen.
• In proteins, the chemical elements present are carbon, hydrogen, oxygen and nitrogen.
• In lipids, the chemical elements present are carbon, hydrogen and oxygen. In some cases, they contain phosphorus, nitrogen, sulfur and other elements.
• Carbohydrates, proteins and lipids are large molecules that are made up from smaller basic units.
• Starch and glycogen are from simple sugars. Protein is from amino acids. Lipids are from fatty acids and glycerol.
• Enzymes increase the rate of chemical reactions without themselves being consumed or permanently altered by the reaction. They also increase reaction rates without altering the chemical equilibrium between reactants and products.
• Factors affecting enzyme activity

  1. As temperature increases to the optimum, the kinetic energy of the enzyme and substrate increases, causing more collisions between the enzyme and substrate

  2. An increase in temperature beyond the optimum causes the enzyme's active site to become denatured (The active site loses its important shape and can no longer form enzyme-substrate complexes, leading to a decrease in enzyme activity)

  3. Deviating from the optimum pH (too high/low) causes the enzyme's active site to become denatured and the active site loses its important shape

  4. The higher the enzyme concentration, the more enzymes there are to form enzymes-substrate complexes, leading to an increase in enzyme activity

  5. Enzyme activity plateaus as there are not enough substrate molecules to react with the extra enzymes
• Diffusion: The net movement of particles from an area of high concentration to an area of low concentration, down a concentration gradient.
• Osmosis: The diffusion of water molecules from an area of high concentration to an area of low concentration through a partially permeable membrane.
• Active transport: The movement of dissolved molecules into or out of a cell through the cell membrane, from an area of lower concentration to an area of higher concentration. The particles move against the concentration gradient, using energy released during respiration.
• Factors affecting the rate of diffusion: The concentration gradient - The greater the difference in concentration, the quicker the rate of diffusion. The temperature - The higher the temperature, the more kinetic energy the particles will have, so they will move and mix more quickly. The surface area to volume ratio - A larger surface area to volume ratio allows for a more efficient exchange of substances with the environment, while a smaller ratio limits the rate of movement.
• Photosynthesis: the process by which green plants and some other organisms transform light energy into chemical energy. They use sunlight to synthesize nutrients from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a by-product.
• Energy cannot be produced or used up, it can only be converted from one form to another. In photosynthesis, light energy is converted into chemical energy which is stored in the sugar molecules produced. This stored energy is then available to the plant cells to use.
• Photosynthesis word equation: carbon dioxide + water (+ sunlight) -> glucose + oxygen
• Symbol equation for photosynthesis: 6CO2 + 6H2O + (sunlight) -> C6H12O6 + 6O2
• Increasing carbon dioxide concentration increases the rate of photosynthesis as it increases the rate of enzyme activity.
• Increasing the light intensity increases the rate of photosynthesis until another factor becomes in short supply (the limiting factor). At very high intensities, photosynthesis is slowed and then inhibited, but these light intensities do not occur in nature.
• At low temperatures, the rate of photosynthesis is limited by the number of molecular collisions between enzymes and substrates. At high temperatures, enzymes are denatured.
• Parts of a leaf: Waxy cuticle, upper epidermis, palisade mesophyll, spongy mesophyll, air space, lower epidermis, guard cells, stoma (stomata pl.)
• A leaf usually has a large surface area, so that it can absorb a lot of light. Its top surface is protected from water loss, disease and weather damage by a waxy layer. The upper part of the leaf is where the light falls, and it contains a type of cell called a palisade cell, which is adapted to absorb a lot of light; Palisade cells contain more chloroplasts than any other plant cells and are more block-shaped so many of them can be packed into the top layer of the leaf. The spongy mesophyll is not packed tightly together, which allows CO2 to reach the palisade cells for photosynthesis.
• Plants require mineral ions for growth and development. Magnesium ions are needed for chlorophyll. Nitrate ions are needed for amino acids.