Organisation
Cells to organ systems: enzymes and digestion, the heart, blood and blood vessels, and transport in plants.
Learn
Organisation, explained point by point
Everything the GCSE specification expects you to be able to do, and how to actually do it - the same lesson a signed-in student studies from.
Describe how cells are organised into tissues, organs and organ systems
Cells of one type group into a tissue (muscle tissue), tissues combine into an organ (the stomach), and organs work together as an organ system (the digestive system). This is levels of organisation, and each level does more than the one below - a single muscle cell cannot digest a meal, but the whole system can.
Explain how enzymes work and what affects their activity
Enzymes are proteins that speed up reactions, each with an active site shaped to fit one substrate - the "lock and key" idea. Warming speeds them up until too much heat changes the active site's shape and the enzyme denatures, stopping it working; each enzyme also has an optimum pH. That is why body enzymes work best around 37 °C.
Describe the human digestive system and the enzymes that break down food
Food travels through the gut while enzymes break large molecules into small soluble ones that can be absorbed. Carbohydrases break starch into sugars, proteases break proteins into amino acids, and lipases break fats into fatty acids and glycerol. Bile from the liver neutralises stomach acid and emulsifies fat into droplets, giving lipase a bigger surface area to work on.
Describe the heart, blood vessels and blood
The heart is a double pump: the right side sends blood to the lungs, the left side pushes it around the body. Arteries carry blood away from the heart at high pressure with thick walls, veins return it at low pressure with valves, and capillaries are one cell thick for exchange. Blood is plasma carrying red cells (oxygen), white cells (defence) and platelets (clotting).
Relate risk factors and lifestyle to non-communicable disease
Non-communicable diseases are not caught from a pathogen - they build up over time. Smoking, a poor diet, too much alcohol and inactivity raise the risk of conditions like heart disease and some cancers. Risk factors often overlap and one can cause another, so scientists look at large populations to separate correlation from a true cause.
Explain transport in plants, including transpiration
Plants have two transport tissues: xylem carries water and minerals up from the roots, and phloem carries dissolved sugars from the leaves to wherever they are needed. Transpiration is the loss of water vapour from the leaves, which pulls a continuous stream of water up the xylem. It speeds up in warm, dry, windy, bright conditions - the same weather that dries washing quickly.
Organisation key terms
The words the specification and the mark schemes use, each defined the way an examiner wants it.
- Tissue
- A group of similar cells working together to carry out a particular function.
- Organ
- A group of different tissues working together to perform specific functions, such as the heart or a leaf.
- Organ system
- A group of organs working together, such as the digestive system, which together make up an organism.
- Enzyme
- A protein that acts as a biological catalyst: it speeds up a reaction without being changed or used up itself.
- Active site
- The region of an enzyme where the substrate binds. Its specific shape is why each enzyme catalyses one type of reaction.
- Denatured
- The state of an enzyme whose active site has changed shape, usually from high temperature or the wrong pH, so the substrate no longer fits.
- Metabolism
- The sum of all the chemical reactions happening in a cell or in the body.
Practice
Try a Organisation question
A GCSE-style original question from this topic. Have a go before you open the working - deciding on an answer first is what makes the working stick.
During exercise a person's cardiac output is 5250 cm³ per minute and their heart rate is 75 beats per minute. Use stroke volume = cardiac output ÷ heart rate to work out the stroke volume, in cm³.
- 70
- 105
- 5325
- 75
Show the answer and the working
Answer: 70
Stroke volume = cardiac output ÷ heart rate, so 5250 ÷ 75 = 70 cm³.
- Cardiac output = heart rate × stroke volume.
- Rearranged: stroke volume = cardiac output ÷ heart rate.
- 5250 ÷ 75 = 70, so the stroke volume is 70 cm³.