Unit 1

• The nucleus can occupy up to 10% of space in an individual cell.
• The nucleus contains DNA and controls the cell's activities.
• The nuclear envelope is the double membrane surrounding the nucleus.
• The nucleus envelope has many nucleus pores, providing access to the nucleus and regulating the transport of molecules such as proteins, RNA and ribosomes.
• The nucleolus is at the centre of the nucleus and produces ribosomes and chromatin (chromosomes in an 'unwound' state).
• There can be more than 1 nucleolus in a nucleus.
• Nucleoplasm maintains the shape and structure of the nucleus.
• Nucleoplasm aids in cellular replication and acts as a suspending substance (where solid particles can be spread throughout liquid without being dissolved) for RNA and DNA.
• What are the 5 uses of water?

  Water is used as a solvent (dissolving molecules so that they can be transported), as a metabolite, for buoyancy, transportation, thermoregulation.
• Water molecules are dipole and polar. The oxygen is slightly negative and the hydrogen atoms are slightly positive.
• Water molecules are covalent bonded, meaning that there are shared pairs of electrons between the atoms. Oxygen is more electronegative than hydrogen so it pulls the shared pair of electrons towards itself, creating an uneven charge across the molecule.
• Water molecules form hydrogen bonds between the slightly negative oxygen atom and the slightly positive hydrogen atom. This is called cohesion. It is important for the transportation of water in plants against gravity.
• Adhesion refers to the attraction between water molecules and xylem walls.
• Cohesion creates surface tension. The water molecules bond together via hydrogen bonds, creating a thin layer on the surface of the water which resists stretching or breaking the surface.
• Polar substances are hydrophilic (water loving) and will dissolve in water.
• Non polar substances are hydrophobic and will not dissolve in water.
• Water is used and released in many different metabolic reactions, such as photosynthesis and hydrolysis. Water also helps move reactants around d the cell for reactions to occur quicker.
• Water must absorb a large amount of heat before its temperature will rise. This is called high specific heat capacity and occurs because of the strong hydrogen bonds between Water molecules. The bonds require a lot of energy (heat) to break before the water molecules can move faster
• A high specific heat capacity means organisms can maintain a constant body temperature, allowing enzymes to work efficiently and ocean temperatures remain stable (within the limits of life)
• A large amount of heat energy must be absorbed for water to turn into vapour. This is called high latent heat of vaporisation and occurs due to the strong hydrogen bonds that require a lot of energy to break. As heat energy is absorbed, water molecules start evaporating, taking heat energy with them and lowering the overall temperature of the organism. This prevents overheating in plants and animals. It also contributes to the stability of large bodies of water.
• Water is transparent. This allows underwater plants to photosynthesize and allows the detection of predators
• Ice forms a crystalline lattice. This pushed the water molecules further apart than when it is in its liquid state and each molecule can bond to a maximum of 4 others. This makes ice 10% less dense than water, meaning that ice floats. This insulates the water below, preventing bodies of water from freezing over and maintaining aquatic life.
• Water is more dense than air so it provides buoyancy and support for water organisms. Plants are turgid and certain organisms can walk on water.
• Viruses are not made up of cells. They lack cell membranes, a nucleus and organelles. Viruses can't reproduce on their own because they don't have the organelles needed to carry out mitosis.
• There are 2 parts to a virus, the protein coat (or capsid) which surroundes the second part of a virus, the genetic material.
• Animal viruses may induce the host cell to co-operate in the infection process. It can bind a receptor on the surface of the cell and can then be taken into the cell via a vesicle during the cell process of receptor mediated endocytosis.
• Plant viruses are unable to penetrate the plant cell wall. For a plant virus to enter its host cell, some kind of mechanical damage must occur, such as if the plant experienced damage from Weather, farming, animals, fire, etc.
• Bacterial viruses bind to the surface receptors and actively insert the genome into the host cell. Unlike the plant virus, bacterial viruses can penetrate through the cell wall.
• There are 4 main shapes of virus: helical, polyhedral, spherical and complex.
• Retrovirus contains RNA instead of DNA as its genetic material. Most retroviruses (like HIV) mutate rapidly, making it difficult to treat.
• Bacteriophages inject bacteria with its genetic material. The genetic material takes over the cell and forces it to make more viruses. When the cell is full of viruses, it bursts and release them.
• The energy source in cells is ATP (Adenosine triphosphate)
• ATP is a nucleotide, containing three phosphate groups, a pentose sugar (ribose) and a nitrogenous base (adenine).
• ATP is used for mechanical work (such as muscle cell contraction and the movement of chromosomes during cell division), transport work (active transport) and chemical work (such as the synthesis of organic chemicals)
• ATP is a good energy source because it produces a manageable amount of energy, small amounts when and where needed. It is an instant source of energy and only 1 enzyme is needed to break down the bond that releases energy.
• A cell can make 2 million ATP molecules per second when needed
• The phosphate groups in ATP are held in place by high energy bonds, so when the bond breaks, it releases a lot of energy.
• Mitochondria is the site of ATP synthesis, therefore the more mitochondria a cell has, the more ATP is produced.
• When ATP releases energy, a bond breaks, separating the molecule from a phosphate group. The ATP becomes ADP. During ATP synthesis, ADP is converted back to ATP through a condensation reaction to an inorganic phosphate.
• An endergonic reaction is when energy is required.