Life Processes at a Cellular Level

• The cell membrane is semipermeable, allowing certain substances to pass through and preventing others from entering.
• The cell membrane prevents dangerous substances from entering the cell and maintains its structure.
• The cell membrane is a phospholipid bilayer, consisting of two layers of phospholipid (a fatty acid chain attached to a phosphate head).
• Inside the cell is cytoplasm, a jelly-like substance filled with nutrients for the organelles.
• Cytoplasm is responsible for suspending organelles of the cell and providing the necessary nutrients to the cell.
• The nucleus is a doubled membrane organelle which protects the DNA within the cell.
• The nucleus is the control centre of the cell which contains genetic information.
• The mitochondria are the place where respiration occurs, with inner and outer membranes which fulfil different roles in respiration.
• The inner membrane of the mitochondria is larger than the outer membrane, causing it to have folds known as cristae, which increase the surface area of the inner membrane.
• The energy created by the mitochondria is used for other processes.
• Different types of cells have a different number of mitochondria depending on how much energy they need.
• Chloroplasts are where photosynthesis occurs, with an inner membrane containing a liquid-filled space called the stroma and thylakoids stacked within it.
• Chloroplasts are only found in organisms that carry out photosynthesis, and the more photosynthesis the plants carry out, the more chloroplasts they tend to have.
• The cell wall is only found in plant cells, giving the cell a rigid shape and structure and having no control over what happens inside and outside of the cell.
• Enzymes are biological catalyst proteins that aid the reaction without being used up, working by an induced fit model where both the active site and the substrate slightly change their shape in order to bind together.
• Enzymes have an optimum temperature and optimum pH which defines the conditions that the enzyme works most effectively at, with different enzymes often having different optimum conditions.
• The collision theory states that particles must collide with enough energy (activation energy) and the right orientation, with increasing the substrate concentration increasing enzyme activity to a certain point before stopping.
• The optimum temperature for most enzymes in the human body is 37 degrees Celsius, with increasing the temperature increases the amount of collisions that occur.
• Once the optimum temperature has been surpassed, the enzyme activity completely stops, as the enzymes have been denatured.
• Denaturing refers to what happens when an enzyme is in an environment that destabilises the enzyme, with the bonds holding the enzyme together beginning to break down, which means the enzyme can no longer hold its structure.
• Endocytosis is when the cell ‘eats’ the large particle by stretching its cell membrane around the big molecule and joining the ends of the membrane to engulf the molecule.
• These types of inhibitors are known as competitive inhibitors as they block the active site and stop the substrate and enzyme from binding together.
• There are two ways to transport material in and out of the cell: passive transport which doesn’t require the use of energy from the cell or active transport which uses the cell’s energy to transport materials.
• Inhibitors that change the shape of the enzyme, therefore affecting the shape of the active site are known as non-competitive inhibitors.
• Oxygen is also produced as a waste product of photosynthesis.
• Photosynthesis is the process of using light energy to convert water and carbon dioxide into glucose for the plant to use as fuel to carry out its life processes.
• The process of photosynthesis occurs in the chloroplast of plant cells.
• Facilitated diffusion involves the use of specific channels and proteins to enable proteins to move from an area where they are in high concentration to an area where they are in low concentration without the expenditure of energy.
• Exocytosis is when the cell ‘spits out’ the large particles by creating special sacs around the substance called vesicles and combining them with the cell membrane.
• Active transport refers to the movement of a substance from a low concentration gradient to a higher concentration, this is done by expending energy (ATP).
• Oxygen is released as a waste product while hydrogen moves to the stroma to be used in the Calvin cycle.
• The light energy breaks into hydrogen and oxygen in the thylakoids.
• Enzymes work most efficiently at an optimum pH which depends on where the enzyme is.
• Enzyme inhibitors are able to compete with the substrates for the active site of the enzyme.
• The enzyme's optimum pH is typically the pH of the environment it operates in.
• Heavy metals such as mercury and lead are a type of enzyme inhibitor that prevents enzymes from carrying out their job.
• When substances can’t be passively transported the cell has three ways to move the substance in and out of the cell: active transport, endocytosis, and exocytosis.
• Enzymes in the stomach have an acidic optimum pH due to the environment they operate in.
• For photosynthesis to occur chlorophyll, which is found inside chloroplasts, needs to be present to trap the sunlight.
• Passive transport includes diffusion which involves a substance moving from an area of high concentration to an area of low concentration, and osmosis which is the transportation of water through a semi-permeable membrane from a high concentration to a low concentration gradient.