Biology (B2) Notes

*Brief notes for the majority of Biology B2 (AQA) from the 2011 specification

Cells

• Living things made of cells
• Structures of cells are related to functions
• Cells are specialised to carry out a job

Cell Structure

• Most cells have:
  • Nucleus - controls activities of cell
  • Cytoplasm - where chemical reactions take place
  • Cell membrane - controls passage of substances
  • Mitochondria - where energy is released in respiration
  • Ribosomes - where protein synthesis occurs
• Chemical reactions are controlled by enzymes in mitochondria (in cytoplasm)

Plant Cells

• Also have:
  • Cell wall - to strengthen the cell
  • Chloroplasts - absorb light to make food
  • Vacuole - filled with cell sap

Other Cells

• Bacterial cells don't have a nucleus, but they have:
  • Cytoplasm
  • Cell membrane
  • Cell wall
• Yeast is a single-celled fungus with:
  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Cell wall

Movement of Substances

• Cells have to replace used substances e.g. glucose + oxygen
• They have to remove waste e.g. carbon dioxide
• Gases and solutions can pass through the cell membrane by diffusion

Diffusion

• The spreading of gas or solution particles
• Movement from an area of high concentration to one of low concentration
• The greater the concentration difference, the faster the diffusion rate

Tissues

• Large multicellular organs develop systems
• As the organisms develop, cells differentiate to perform different jobs
• Tissues are groups of cells with a similar structure + function, e.g:
  • Muscular tissue contracts to bring about movement
  • Glandular tissue produces substances
  • Epithelial tissue covers organs

Organs

• Made of tissues; may contain several
• E.g. the stomach contains:
  • Musclular tissue to churn contents
  • Glandular tissue to produce digestive juices
  • Epithelial tissue to line and cover the stomach

Organ Systems

• Groups of organs that carry out a function, e.g. the digestive system:
  • Pancreas + salivary glands to produce digestive juices
  • Stomach + small intestine where digestion occurs
  • Liver to produce bile which breaks down fat
  • Small intestine where soluble food is absorbed into the blood
  • Large intestine where water is absorbed, producing faeces
• Humans have other organ systems e.g. excretory, circulatory and reproductive systems

Plant Organs

• Stems, roots and leaves
• Tissues include:
  • Epidermal substances to cover the plant
  • Mesophyll where photosynthesis occurs
  • Xylem and phloem to transport substances

Photosynthesis

• Plants make food using sunlight
• Occurs in light-exposed cells
• Light energy absorbed by chlorophyll (found in chloroplasts)
• Four things needed:
  • Light
  • Carbon Dioxide
  • Water
  • Chlorophyll
• Light energy converts carbon dioxide + water into glucose + oxygen (a by-product)
• carbon dioxide + water → glucose + oxygen
•  6CO₂  +  6H₂O  →   C₆H₁₂O₆  +  6O₂

How Plants Use Glucose

• Glucose from photosynthesis may be:
  • Stored as insoluble starch
  • Used in respiration
• Some is used to produce:
  • Fat + Oil
  • Cellulose ( to strengthen cell walls)
  • Proteins
• Proteins are also produced using nitrate ions from the soil.

Factors Affecting Photosynthesis

• Temperature
• Carbon dioxide concentration
• Light intensity

Temperature

• As temperature increases, so does the rate of photosynthesis
• At 45 C the rate drops to zero; enzymes have been destroyed

Carbon Dioxide Concentration

• As the concentration…