Biology

• We have 8 characteristics of living things.
• These are ✨️

  Movement. Homeostasis

  Respiration. Reproduction

  Sensitivity. Excreation

  Growth. Nutrition
• Examples of homeostatic mechanisms include maintaining blood glucose concentration, temperature regulation, and pH balance.
• Movement- it is the ability of an organism, or part of it to change position or place.
• Respiration- it is a chemical reaction in cells which break down nutrient molecules and releases energy for metabolism.
• Sensitivity - it is the ability to detect changes in the environment and respond to them.
• Growth - the permanent increase in size and dry mass.
• Reproduction-process when organisms make more of the same kind of organism.
• Excretion- removal of waste products of metabolism and substance in excess requirements. E.g carbon dioxide
• Nutrition-taking in materials for energy, growth and development.
• Homeostasis-the maintenance if a constant internal body environnement e.g blood PH and body temperature
• Cell


  The smallest part of a living organism
• Animal cell components


  • Cell membrane
  • Nucleus
  • Cytoplasm
  • Small vacuoles
  • Mitochondria
  • Ribosomes
• Plant cell components


  • Cell wall
  • Nucleus
  • Cell membrane
  • Chloroplasts
  • Vacuole
  • Cytoplasm
• Animal cell


  • Cell membrane is a very thin layer of protein and fat
  • Cell membrane is partially permeable, allowing some substances to pass through but not others
  • Cytoplasm is a clear jelly, watery fluid, made of 70% water and containing dissolved substances especially proteins, where many metabolic reactions take place
  • Small vacuoles are called vesicles and contain different solutions
  • Mitochondria are sausage shaped and synthesise energy (ATP)
  • Ribosomes are tiny structures found in cytoplasm responsible for making protein
  • Nucleus is a dark, deeply stained organelle which contains genetic information: DNA
• Plant cell


  • All organelles mentioned in animal cell are present
  • Cell wall is made up of cellulose, a polysaccharide, forming a very strong casing to protect and support the cell
  • Cell wall stops the cell from bursting if it absorbs a lot of water
  • Cell wall is fully permeable
  • Large, permanent vacuole contains cell sap - a solution of sugars
  • Chloroplasts are disc shaped and contain chlorophyll which absorbs light energy from the sun and uses it to make starch for the plant by photosynthesis
  • Chloroplasts may also contain starch grains
• Bacterial cell


  • Unicellular (single celled)
  • Have a peptidoglycan cell wall
  • Have a selectively permeable cell membrane
  • Have cytoplasm and ribosomes
  • Do not have mitochondria or chloroplasts
  • Do not have a nucleus
  • Have naked DNA, not bound to chromosomes, lying in cytoplasm
  • Also have a circle of DNA called plasmids
  • May have a capsule made of cellulose
• Levels of organisation


  • Cells
  • Tissue
  • Organ
  • Organ system
  • Organism
• Tissue


  A group of cells that have the same function
• Organ


  A group of different tissues that carry out the same function
• Organ system


  Different organs which perform the same function, e.g. digestive system
• Specialised cells


  • Cells grow and mature, developing adaptations to enable them to perform their functions better
• Examples of specialised cells

  • Ciliated cells
  • Red blood cells
  • Nerve cells
  • Sperm cells
  • Egg cells
  • Palisade cells
  • Xylem vessels
  • Root hair cells
• Ciliated cells


  • Found in airways, move mucus (containing dust/bacteria) away from lungs
  • Have cilia - cytoplasmic extensions that move rhythmically
  • Have many mitochondria for energy for movement
  • Positioned near goblet cells that produce mucus
• Red blood cells


  • Found in the blood
  • Contain haemoglobin (red pigment to carry oxygen)
  • No nucleus - so more space for more oxygen
  • Biconcave shape increases surface area for faster oxygen diffusion
• Nerve cells


  • Composed of neurones
  • Long to reach all body organs
  • Many dendrites to connect to other neurones
  • Plenty of mitochondria to provide energy for the transmission of impulses
• Sperm cell


  • Has a haploid nucleus
  • Has a tail to swim toward the egg
  • Plenty of mitochondria
  • Acrosome contains enzyme to dissolve the jelly coat on the egg
• Egg cell


  • Stationary
  • Haploid nucleus
  • Plenty of cytoplasm to nourish the zygote
  • Cell membrane, cytoplasm containing yolk, and nucleus containing chromosomes
• Palisade cells


  • Large, permanent vacuole
  • Many chloroplasts to convert light energy into chemical energy faster
  • Upright to help the light get into the leaf
  • Tightly packed to catch all the sunlight
• Xylem vessels


  • No cell contents, allowing more space for water and less resistance to water flow
  • Arranged in an end-on-end to form a continuous tube with less resistance
  • Cell walls strengthened with lignin to provide support for the plant
• Root hair cells


  • Root hair extension increases the surface area for faster absorption of water and minerals
  • Many mitochondria for energy for active uptake of mineral salts
• Magnification


  How many times an object has been enlarged
• 1mm = 1000 micrometers (μm)
• Actual size = Magnification x Image size
• What are enzymes primarily made of?

  Proteins
• What is the role of enzymes in chemical reactions?

  They speed up chemical reactions
• Why are enzymes sometimes referred to as metabolic reactions?

  Because they can control metabolic reactions
• What are the three types of enzymes mentioned?

  • Protease
  • Lipase
  • Amylase
• What happens to enzymes at extreme temperatures?

  They denature, preventing the substrate from fitting in the active site
• What is the optimum pH for enzyme activity?

  pH 7