Biology Year 9 (all)

SPECIALISED CELLS

NERVE CELL aka neuron. in the nervous system across the whole body, mostly in brain and spinal column. To send and receive electric messages to and from the brain. They have a long, thin shape, and their axon is covered by a myelin sheath.

MUSCLE CELL found in muscles all around the body. Have many mitochondria to hold more energy. Contain myglobin (which stores oxygen) to prevent aerobic respiration.  

PALISADE CELL found on the top half of a leaf. Made to carry out photosynthesis so it has many chloroplasts. The vacuole pushes chloroplasts to the edge of the leaf.

XYLEM CELL makes up the xylem tubes in plants. To carry water and minerals through stem to leaves. Made of dead cells which form hollow tubes, which are lined with lignin to make them waterproof. No organelles.

ROOT HAIR CELL found in plant roots. To absorb water and nutrients from the soil. Has long, thin hair to give a larger surface area. Thin cell wall so water can pass through. Large vacuole to store water.

INSIDE CELLS

NUCLEUS contains cell's DNA.

CYTOPLASM in which most chemical reactions take place.

CELL MEMBRANE controls the passage of substances into and out of the cell. MITOCHONDRIA aerobic respiration takes place here.

RIBOSOMES on which protein synthesis takes place.

CHLOROPLASTS absorb light energy to photosynthesize. PLANT ONLY

PERMANENT VACUOLE contains cell sap. PLANT ONLY

CELL WALL strengthens the cell and maintains its rigid structure. PLANT ONLY

CHEMICAL REACTIONS IN CELLS

• Respiration - the release of energy from glucose.
• Photosynthesis - the production of glucose using light energy.
• Protein synthesis - build up of large proteins from smaller molecules.

CELL METABOLISM the rate at which chemical reactions occur in cells.

TYPES OF CELLS

• Eukaryotes - plants, animals, fungi, and protoctis. all organelles are membrane-bound. larger.
• Prokaryotes - bacteria. DNA floats free in the cytoplasm. no membrane-bound organelles. smaller.

DIFFUSION AND OSMOSIS

DIFFUSION the spreading out of particles of any substance across a membrane, going from an area of high to an area of low concentration.

• can be in solution or gas.
• a passive process.
• affected by:
  • concentration gradient - the bigger the difference in concentration on one side vs the other, the faster diffusion occurs.
  • temperature - the higher the temp, the faster the rate. more kinetic energy.
  • surface area - greater surface area, more molecules can cross at same time. occurs faster.
  • distance - shorter exchange surface, faster diffusion occurs.
• used by glucose and oxygen to move in and out of cells.
• oxygen moves into bloodstream.

OSMOSIS the net movement of water from high to low concentration across a partially permeable membrane.

• hypotonic solution - in hypo, the concentration is higher outside than in, so lots of water…