Structures and Functions in Living Organisms

Structures and Functions in Living Organisms

1. Levels of Organisation

   • Organelles - Small organs in cells
   • Cells - Biological building blocks
   • Tissues - Groups of similar cells that do the same job
   • Organ - Made of different tissues that work together to do a specific job
   • Organ Systems - Multiple organs that work together
   • Organism - A living being made of multiple organ systems

2. Cell Structure

   • Nucleus - Controls the cell and contains DNA
   • Cytoplasm - Jelly-like substance in cells where reactions occur
   • Cell Membrane - Holds the cell in and allows certain particles in/out
   • Cell Wall (plant only) - Supports and protects the cell
   • Chloroplast (plant only) - Contains chlorophyll which enables photosynthesis to occur
   • Vacuole (plant only) - Contains water and sugars needed for cell growth

3. Nutrition

   • Photosynthesis is the conversion of sunlight into food for a plant
   • Water + Carbon Dioxide (+ energy) -> Oxygen + Glucose ¦¦¦ 6H2O + 6CO2 (+ energy) -> 6O2 + C6H1206
   • Limiting Factors - CO2 concentration, temperature and light intensity
     • Lower CO2 concentration reduces the rate of photosynthesis
     • Lower light intensity reduces the rate of photosynthesis
     • Lower temperature reduces the rate of photosynthesis
   • Leaves are adapted for photosynthesis
     • Upper epidermis is transparent to let light through
     • Palisade cells are near the top of the leaf where there is the most light
   • Mineral ions are needed for growth
     • Magnesium is needed for chlorophyll
     • Nitrates are needed for amino acids

4. Transport

   • Blood = Red + White blood cells, platelets and plasma
   • Plasma carries CO2, digested food, urea, hormones and heat
   • Red blood cells are adapted to carry oxygen
     • They are biconcave to increase surface area
     • They have no nucleus to free up space for oxygen
     • They contain haemoglobin which binds reversibly with oxygen (forming oxyhaemoglobin)
   • White blood cells provide immunity to disease
     • If they detect a pathogen, they produce antibodies to destroy it
       • Antibodies stick to pathogens making them easy to identify by phagocytes, which ingest the pathogens (phagocytosis)
       • Antibodies cause pathogens to stick together making it easier for phagocytes to ingest them
       • This also applies to weakened/dead strains, allowing for safe vaccinations
     • After destroying a pathogen they produce memory cells which retain information about the pathogen so they can be destroyed more efficiently next time
   • Platelets help blood to clot. Clotting prevents blood loss and entry of microbes
   • You need to know the structure of the heart (4 chambers, blood vessels and valves)
     • The heart beats faster (pumping more blood) during exercise or under the effect of adrenaline, to meet the body's demand for oxygen
   • Arteries carry blood AWAY from the heart at high pressure
   • Veins carry blood totheheart at low pressure
   • Capillaries link arteries and veins, and have thin walls to allow gas exchange with cells
   • In Plants
     • Phloem transports sucrose and amino acids between parts of the plant that need them
     • Xylem transports water and mineral ions from the roots to the leaves
       • This is done by a process called transpiration, where water evaporates off the leaves to drag more up
         • Humidity, wind speed, temperature and light intensity all affect the rate of transpiration positively (except humidity, which affects it negatively)
     • Water is absorbed by root hair cells via osmosis

5. Respiration

   • Releases energy from food
   • Aerobic respiration requires oxygen, but is very efficient
   • Anaerobic respiration does not need oxygen but it is very inefficient and produces lactic acid in animals
   • Oxygen + Glucose -> Water + Carbon Dioxide (+ energy)

6. Gas Exchange

   • Ribs protect the lungs and heart
   • Intercostal muscles located between ribs expand and contract during breathing
   • Diaphragm contracts during inhalation to allow lungs to expand and take in air
   • Trachea = Windpipe - Connects mouth and lungs
   • Lungs made of bronchi (branches) which split into bronchioles, ending in alveoli
     • Alveoli are tiny air sacs surrounded by capillaries which allows for gas exchange between blood and the lungs
       • They have a large surface area in contact with the capillaries to maximise gas exchange
   • In Plants
     • When the rate of photosynthesis exceeds the rate of respiration, there is a net release of oxygen. When the rate of respiration exceeds the rate of photosynthesis, there is a net release of carbon dioxide.
     • Net exchange of oxygen and carbon dioxide depends on light intensity.
     • The stomata are pores on the underside of leaves. They open and close to let water and oxygen out, and carbon dioxide in.

7. Movement of Substances in Cells

   • Diffusion is the net movement of particles from an area of high concentration to low concentration, down the concentration gradient
   • Osmosis is the net movement of water particles from an area of high concentration to low concentration, down the concentration gradient, across a selectively permeable membrane
   • Active Transport is the net movement of particles from an area of low concentration to high concentration, against the concentration gradient. It is an active process and requires energy.
   • The surface-area-to-volume ratio, temperature and concentration gradient all affect the rate of movement

8. Nutrition Continued

   • A balanced diet needs appropriate proportions of proteins, carbohydrates, lipids, vitamins, minerals, water and fibre
     • Starches give long-lasting energy Sugars give short bursts of energy
     • Proteins are needed for amino acids, which are needed for growth and repair
     • Fats are a store of energy and also provide insulation and protection
     • Vitamin A strengthens the immune system
     • Vitamin C protects cells and helps blood clotting
     • Vitamin D helps regulate calcium and phosphate levels and strengthens bones
     • Calcium helps blood clotting and strengthens bones
     • Iron helps make red blood cells
     • Water is needed for hydration
     • Fibre is needed for a healthy alimentary canal
   • Energy needs vary depending on age, activity level and pregnancy.
   • You need to know the structure of the alimentary canal (digestive system)
   • Peristalsis is the movement of ring muscles to push food along the gut
   • Bile is made by the liver and stored in the gall bladder. It neutralises stomach acid and emulsifies lipids
   • The intestines have very large amounts of villi, which have a large surface area and produce digestive enzymes, to absorb products of digestion efficiently