Biology: Chapter 1

Brief notes on Chapter 1: Life Processes

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Life Processes

All living organisms:

  • Require Nutrition - either make own food (plants via photosynthesis) or eat other organisms.
  • Excrete* - the removal of the waste products of cells.
  • Move - Growth movements in plants (e.g. phototropism) and the action of muscles in animals.
  • Grow and Develop - increase in size and mass from the materials in food.
  • Respire - obtaining energy from their food.
  • Respond to Stimuli - sensitivity to change in external environment.
  • Reproduce - produce offspring.
  • Control - change internal conditions (homeostasis).

* Do not confuse with egestion (the removal of faeces).

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Cell Structure

  • Cytoplasm - living material which makes up the cell.
  • Nucleus - controls activities which take place in the cell, contains chromosomes which carry the genes of the organism.
  • Cell Membrane - partially permeable so that some chemicals can pass through it but others cannot. It controls what substances can pass in either direction.
  • Mitochondria - these carry out some of the reactions of respiration.
  • Cell Wall - Made up of cellulose and helps the cell maintain its shape. It is freely permeable.
  • Vacuole - a store of dissolved sugars, mineral ions and other solutes.
  • Chloroplasts - these absorb light energy in the process of photosynthesis. They contain chlorophyll so they are green; any part of a plant which is not green, has no chloroplasts.
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Enzymes are a group of proteins which control chemical reactions in a cell. They are biological catalysts (they speed up reactions) and do not change after the reaction.

The molecule an enzyme acts on is called the substrate which fits into the enzyme's active site. The reaction takes place so teh substrate breaks down to form the products.

Enzymes have an optimum temperature and pH - the temperature and pH where the enzymes works most efficiently. Most enzymes in humans work best at about body temperature (37˚C). At any temperature after its optimum level, the enzyme begins to denature*.

*Not 'die'.

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Cell Respiration

Aerobic Respiration:

Glucose + Oxygen --> Carbon Dioxide + Water (+ Energy)

C₆H₁₂O₆ + 6O₂ --> 6CO₂ + 6H₂O (+ Energy)

Anaerobic Respiration:

Glucose --> Ethanol + Carbon Dioxide (+ Some Energy)

C₆H₁₂O₆ --> 2C₂H₅OH + 2CO₂ (+ Some Energy)

Anaerobic Respiration in Yeast:

Glucose --> Lactic Acid (+ Some Energy)

C₆H₁₂O₆ --> 2C₃H₆O₃ (+ Some Energy)

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Movement of Materials In and Out of Cells

Cell respiration requires that cells are able to take in certain substances in (such as glucose and oxygen) and get rid of others (such as water and carbon dioxide).

The cell membrane is selectively permeable and the main ways that molecules and ions can get through it are by diffusion, active transport and osmosis.

Diffusion occurs when a substance moves (due to kinetic energy) from a high concentration of that substance to a lower concentration. The substance goes down a 'concentration gradient'.

Active transport is when the substance moves against a concentration gradient and osmosis is diffusion specific to water.

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