Cells, Classification and Life Processes: notes

Living Things and Classification

• Characteristics of living things: living things move, respire, respond to stimuli, excrete waste, feed (nutrition), grow, reproduce, and are made of cells. Use the word MRS GREN to remember them.
• Kingdom: the largest group in the classification system. Main kingdoms include Animalia, Plantae, Fungi, Protista and Monera.
• Vertebrate classes: fish, amphibians, reptiles, birds and mammals. Mammals have hair and feed their young on milk.
• Flowering plants: plants that make flowers and seeds. They are split into monocots (one seed leaf) and dicots (two seed leaves).
• Simple key: a set of yes/no questions that leads you to the name of an organism. Each question splits the group in two.

Cells, Tissues and Organs

• Plant cell: has a cell wall, cell membrane, cytoplasm, nucleus, large permanent vacuole and chloroplasts.
• Animal cell: has a cell membrane, cytoplasm, nucleus and mitochondria. It has no cell wall, no chloroplasts and no large vacuole.
• Specialised cell: a cell with a shape suited to its job. A root hair cell has a long projection to absorb water. A red blood cell has no nucleus to carry more oxygen.
• Tissue to system: cells form tissues, tissues form organs, and organs form organ systems, such as the digestive system.

Microscopes and Magnification

• Magnification: how many times bigger an image looks compared with the real object.
• Total magnification: eyepiece lens magnification multiplied by objective lens magnification.
• Worked example: a cell looks 5 mm long under a microscope at ×400. Actual size = image size ÷ magnification = 5 mm ÷ 400 = 0.0125 mm.

Diffusion, Osmosis and Active Transport

• Diffusion: the movement of particles from a high concentration to a low concentration, with no energy needed.
• Osmosis: the movement of water molecules across a partially permeable membrane, from a dilute solution to a concentrated one.
• Active transport: the movement of particles against a concentration gradient, from low to high concentration. It needs energy from respiration.

Enzymes

• Enzyme: a biological catalyst made of protein. It speeds up a reaction without being used up.
• Optimum temperature: most human enzymes work best at about 37°C.
• Denaturing: very high temperatures or extreme pH change the enzyme's shape, so the active site no longer fits the substrate. The enzyme stops working.

Common Slips

• Plant vs animal cell: do not forget the cell wall, chloroplasts and vacuole belong to plant cells only.
• Magnification: divide by magnification to find actual size. Do not multiply.
• Osmosis vs diffusion: osmosis only refers to water and needs a partially permeable membrane.
• Enzymes: low temperature slows enzymes down but does not destroy them. High temperature destroys them.