All living things are made up of cells.
HUMAN CELLS HAVE:
- a nucleus which controls the activities of the cell
- cytoplasm where most of the chemical reactions (controlled by enzymes) take place
- a cell membrane which controls what passes in and out of the cell
- mitochondria where most energy is released from respiration
- ribosomes where protein synthesis happens
PLANT CELLS HAVE:
- a cell wall that strengthens the cell, keeping them turgid to withstand pressure
- chloroplasts that absorb light energy to make food
- a permanent vacuole filled with cell sap
Cells may be specialised to carry out a particular function e.g. root hair cells are long and thin, sperm cells have long tails, red blood cells have large surface areas.
Diffusion & Osmosis
To get into and out of cells, dissolved substances have to cross cell membranes.
Dissolved substances can move into and out of cells by DIFFUSION and OSMOSIS
e.g. oxygen required for respiration passes through cell membranes by diffusion and water often moves across boundaries by osmosis.
- is the spreading of particles in a gas or substance in solution until they are evenly spread out
- it involves a net movement from a region of high concentration to lower concentration
- the greater the difference in concentration, the greater the rate of diffusion
- is the diffusion of water from a dilute to a more concentrated solution via a partially permeable membrane (which allows the passage of water molecules)
- differences in the concentrations of the solutions inside and outside a cell cause water to move into or out of the cell by osmosis
Green plants use light energy to make their own food. They obtain the raw materials they need to make this food from the air and soil.
CARBON DIOXIDE + WATER (+LIGHT ENERGY) >>> GLUCOSE + OXYGEN The glucose produced may be be converted into insoluble starch that is stored in the roots. Plant cells use some of the glucose produced during photosynthesis for respiration.
THE RATE of photosynthesis may be limited by: LOW TEMPERATURES, a SHORTAGE of CARBON DIOXIDE and a SHORTAGE of LIGHT
- a thin shape so that gases diffuse easily
- a large surface area for maximum absorption of sun light rays
- chloroplasts containing chlorophyll for absorption
- veins which support the leaf and carry substances to/from cells
PLANT ROOTS absorb mineral salts for healthy growth.
- nitrates - to produce amino acids - used to form proteins - DEFICIENCY = STUNTED GROWTH
- magnesium - to produce chlorophyll - DEFICIENCY = YELLOW LEAVES
Energy & Biomass
All plants and animals eventually die. Microbes play an important part in decomposing materials so that it can be used again by plants. The same material is recycled over and over.
- Living things remove materials from the environment for growth and other processes. These materials are returned to the environment in waste materials or when they die and decay
- Materials decay because they are DIGESTED (broken down) by micro-organisms which digest materials faster in WARM & MOIST conditions where there is plenty of OXYGEN.
THE CARBON CYCLE:
- CARBON DIOXIDE is removed from the environment by green plants for photosynthesis to make carbohydrates, fats and proteins.
- some carbon dioxide is returned to the atmosphere when green plants respire.
- green plants are eaten by animals and those animals are eat by other animals so the carbon becomes fats and proteins that make up the animal's bodies.
- CARBON DIOXIDE is returned to the atmosphere when animals respire.
- micro-organisms feed on the bodies of the dead animals and they release carbon dioxide when they respire