biology st2 (year 9)

• All living things are built from smaller units called cells
• Organelles and their roles

  • Nucleus - controls the activities of the cell
  • Cytoplasm - where the chemical reactions of the cell take place
  • Cell membrane - controls the movement of substances into and out of the cell
  • Mitochondria - where respiration occurs to release energy for the cell
  • Ribosomes - where proteins are synthesised (made)
• Plant cell organelles

  • Chloroplasts - absorb light energy for photosynthesis (contains chlorophyll which is a green )
  • Vacuole - filled cell sap, which also helps support the plant cell
  • Cell wall - made out of a tough substance called cellulose, strengthens and supports the cell
• Bacteria

  Single-celled organisms, much smaller than animal or plant cells (approx. 1μm)
• Bacterial cells

  • Have a cytoplasm, surrounded by a cell membrane and cell wall
  • Have no nucleus
  • Genetic material is found free in the cytoplasm
  • Many (not all) bacteria contain plasmids, which are small circular bits of DNA
• Prokaryotes

  Genetic material is not enclosed in a membrane-bound nucleus, have circular DNA called plasmids
• Eukaryotes


  Genetic material is enclosed in a membrane-bound nucleus, have lots of organelles enclosed in membranes
• Cell Examples

  • Prokaryotes: Bacteria, archae
  • Eukaryotes: Animal, plant, fungi
• Prokaryotes are much smaller (approx. 1 μm across) than eukaryotes (approx. 10-100 μm across)
• The nucleus contains the genetic material (DNA) that controls all cellular activities.
• Preclinical stages

  1. Tested on cells and possibly animal (whole body system)

  2. Ensures toxicity is not prevalent
• Clinical stage

  1. Tested on small groups of healthy volunteers to check for side effects

  2. Tested on larger groups of healthy volunteers to check for side effects again, less risk for volunteers and to avoid drug interactions

  3. Tested on small group of patients with the disease to check dose and efficacy

  4. Tested on larger group of patients to allow adverse reactions and reliable results
• Drug development

  1. Effective (must prevent or cure a disease)

  2. Safe (must not be toxic or poisonous, unacceptable side effects)

  3. Stable (must be able to be stored for a sufficient length of time without changing chemical structure under normal conditions)

  4. Easily taken in and removed from the body
• All new medicines must be extensively tested and trialed
• It can take up to 12 years to take a drug from the development stages to a doctor's surgery
• Production of a new drug can cost millions of pounds
• Using a microscope

  1. Place slide on stage and secure using stage clips

  2. Use lowest magnification objective lens

  3. Turning the coarse knob to move the stage closer to objective lens

  4. Look through eyepiece and focus coarse knob until the cells focus

  5. Change to a higher magnification objective lens

  6. Slightly rotate the fine adjustment knob to bring cells into a clear focus and use a higher objective lens to view cells more clearly

  7. Make a clear, labelled diagram of these cells
• Magnification

  How much you can enlarge an image
• Resolving power


  Ability of the microscope to distinguish between objects
• Resolution

  Ability to distinguish between two objects on an image
• Field of view

  Area that you can see under a microscope
• Stages of a vaccination

  1. Inject an inactive or dead pathogen (in small quantities)

  2. Antigens in the vaccine stimulate white blood cells to make antibodies

  3. If re-infected, white blood cells produce correct antibodies rapidly

  4. Pathogen population too low to cause disease
• The mitochondria produce energy through respiration.
• The nucleus contains genetic material which controls cell activity.
• Ribosomes are responsible for protein
• Chloroplasts contain chlorophyll and carry out photosynthesis.
• How pathogens enter our body

  • Droplet infections
  • Direct contact
  • Contaminated produce
  • Breaks in the skin
• White blood cells

  • Defend against pathogens by phagocytosis (engulf+digest)
• Examples of non-lifestyle cancer risks are: age and
• Lifestyle factors like smoking, obesity, viruses, alcohol, uv radiation and exposur to carciogenic chemicals can increase cancer risk.
• Benign tumour

  Slow growing, often have a tough capsule, not cancerous and rarely spread
• Malignant tumour

  Faster growing, can spread through other body tissues, can form secondary tumours
• Non-communicable diseases cause more deaths worldwide than communicable diseases
• Risk factors can increase the chance of a person having a non-communicable disease
• Antibiotics should only be used for bacterial infections, not viral infections
• Stem cells

  • Unspecialised cells with potential to differentiate into many cell types
  • Very few in adult bodies
  • Can be used to treat diseases and injuries
  • Controversial use of embryonic stem cells
• Stem cells can be found in the tips of plant roots and shoots (meristem tissue)
• Cancer is the uncontrolled growth of a mutation in a cell, dividing uncontrollably.
• A tumour is an abnormal mass of tissue that results from excessive cell division
• Malignant tumours:

  • faster growing
  • can spread through other body tissues
  • can form secondary tumours