1. Cells, and what they do

2. The signs of life Processes that are characteristic of all living organisms MMovement All living things move, even plants RRespiration Getting energy from food SSensitivity Detecting changes in the surroundings GGrowth All living things grow RReproduction Making more living things of the same type EExcretion Getting rid of waste NNutrition Taking in and using food CControl of the internal environment, e.g. temperature, pH

3. Levels of organisation The basic unit of life is the cell. All living things are made of cells Cells are all specialized to perform special functions. Cells also contain organized structures (organelles) In multicellular organisms, cells also belong to higher levels of organisation … as follows

4. organelle to organism Organism: a living creature - e.g. a bacterium, a yeast cell, a plant or an animal. Organ system: different organs that work together for a specific function. Organ: different tissues that function together to do a certain job Tissue: similar cells that work together Cell: the smallest unit of life that is able to carry out all the functions of living things Organelle: a structure within a cell that performs a particular function within the cell

5. Biological Molecules At a still lower level of organization. A molecule consists of different atoms joined together by chemical bonds. Examples include DNA, glucose, starch, proteins, chlorphyll, oxygen, carbon dioxide. Proteins: MANY kinds. Responsible for the structures and metabolism of cells and organisms.

6. Organelles: In animals AND plants, the cell has: a nucleus a cell membrane cytoplasm mitochondria

7. A section through a liver cell (animal cell): cell membrane cytoplasm nucleus DNA controls what enters and leaves the cell metabolic (chemical) reactions occur here contains the DNA, controls the cell contains instructions to make proteins

8. The nucleus Genes in the nucleus are sections of DNA The genes control the activities of the cell by determining which proteins the cell can make Genes are responsible for the differences between species and between individuals in the same species Genes are inherited from both parents

9. The cell membrane The cell membrane surrounds the cell. It is semi-permeable (meaning it lets some molecules through, but not all). Another term for semi-permeable is selectively permeable. The membrane controls which substances pass into and out of a cell.

10. Cytoplasm is a jelly-like substance that fills cells It contains a network of complex structures Metabolism (i.e. all the chemical reactions of the cell) takes place there

11. The mitochondrion The later steps in aerobic respiration happen in the mitochondrion They are found in all complex cells (plants and animals) Cells that use a lot of energy may contain thousands of mitochondria

12. Plant cells Plant cells - but not animal cells - also contain: a cell wall a permanent central vacuole chloroplasts (in the green parts of the plant only)

13. Section through a palisade cell of a leaf (plant cell) cell membrane nucleus cytoplasm chloroplast large vacuole cellulose cell wall

14. The cell wall The cell wall of plants is freely permeable and made of cellulose It lets water and other molecules through freely It protects the contents of the cell It works with the vacuole to support the cell

15. The vacuole The vacuole is filled with cell sap The vacuole attracts water by osmosis, which makes it fill and press against the cell wall, which gives the tissues and organs of the plant support so that it stands up This phenomenon (stiffness due to filling with water) is called turgor

16. Chloroplasts Chloroplasts absorbs light energy to make food by photosynthesis The chloroplast contains a chlorophyll, which is the molecule that traps the light They are found in leaves – particularly in the palisade cells – and other green parts of plants

17. Cell division and differentiation Multicellular organisms begin life as a single cell called a zygote From the zygote, growth results from cell division, which is performed by a process called mitosis In mitosis, the chromosomes double (before it starts), the nucleus splits in two and then the cytoplasm divides The process produces two cells with identical genes

18. Differentiation Different kinds of cells are produced as the embryo grows, a process known as differentiation Through differentiation, cells in both animals and plants can specialize for a particular function The basic principle is specialized structures enable specialized functions - we say that cells are adapted to carry out particular functions

19. Specialized Cells in Animals muscle cells can contract to enable movement and support sperm cells can move fast (for their size) to fertilize an egg nerve cells conduct electrical impulses quickly over large distances

20. Specialized Cells in Plants root hair cells have a large surface area to absorb water and minerals efficiently leaf palisade cells contain many chloroplasts to convert light energy to chemical energy xylem vessels carry water efficiently up long stems root hair

21. Respiration Respiration releases energy for muscle contraction, active transport of molecules and ions, building large molecules, cell division The energy is generated in the form of a molecule called ATP, which then transfers its energy to other processes Aerobic respiration is performed in virtually all complex cells, and provides a large amount of ATP Anaerobic respiration is respiration in the absence of oxygen. It produces relatively little ATP

22. Aerobic respiration The process begins in the cytoplasm but is completed in the mitochondria The symbol equation is: C 6 H 12 0 6 + 6O 2 -> 6CO 2 + 6H 2 O The word equation is: glucose + oxygen -> carbon dioxide + water

23. Anaerobic respiration In anaerobic respiration, glucose is not completely broken down and produces toxic waste products are produced Yeast cells are an example of micro-organisms that perform anaerobic respiration when oxygen is in short supply Micro-organisms perform a type of anaerobic respiration called fermentation Muscle cells are an example in humans of cells that perform anaerobic respiration when oxygen is in short supply

24. Fermentation Yeast cells and bacteria perform a type of anaerobic respiration known as fermentation The products are ethanol (commonly known as alcohol) and carbon dioxide The equation is: glucose -> carbon dioxide + ethanol Fermentation is the process used to make beer and sparkling wine – and also black tea, so it’s not only about alcoholic drinks!

25. Anaerobic respiration in humans Muscle cells are an example in humans of cells that perform anaerobic respiration when oxygen is in short supply Lactic acid is produced, and diffuses into the blood The lactic acid is broken down in the presence of oxygen The equation is simple: glucose -> lactic acid Anaerobic respiration supplies energy for intense exercise over short periods, e.g. weight-lifting and sprinting

26. Enzymes Enzymes are made of protein, which allows them to have many different forms They catalyse reactions – each enzyme is specific for a particular reaction, and every metabolic process is controlled by enzymes

27. Enyzme-controlled reactions The substance that is acted on is called the substrate – it binds to the active site of the enzyme and is converted to a product The reactions of enzymes work fastest at a particular (optimum) temperature and pH In humans, the optimum temperature is 37ºC, but in reptiles, for example, an enzyme might work best at a lower temperature

28. Optimum temperature and pH At low temperatures, kinetic energy is low, and there is less contact and less force in binding between substrate and active site At high temperatures, the enzyme loses its shape – is denatured – so the active site is no longer active Enzymes also have an optimum pH, e.g. in the stomach, pepsin has the optimum pH of around 2, so it is adapted to its environment

29. Experiments on enzymes We can test enzymes by seeing either how much product is made or how much substrate is consumed in a particular time. For example, in the amylase experiment, we checked how long it took for all the substrate (the starch) to be consumed. To test for the presence of starch we used an indicator, iodine.