Patterns in Nature

1. Patterns in Nature

2. Cell theory • Cells are the smallest living units of organisms • All cells come from pre-existing cells. • Each organism is made of one or more cells.

3. Evidence to support cell theory Cell theory was formulated over a period of about 300 years in parallel with the development of the microscope. Microscopes enabled scientists to make observations of tissues from organisms. As microscopes improved scientists began to study the internal structure of cells and identify cell organelles.

4. Development of Cell Theory • 1590 The first compound (two lens) microscope was made by Hans and Zacharias Janssen. • 1665 Robert Hooke studied thin slices of cork under the microscope and described what he saw as small boxes or cells. • 1676 Anton van Leeuwenhoek, saw microorganisms under the microscope when he viewed a few drops of pond water.

5. Development of Cell Theory • 1824 Frenchman Henri Dutrochet suggested that all organisms are composed of cells. • 1827 Scottish botanist, Robert Brown discovered and described the nucleus in plant cells. • 1838 German biologists Schleiden and Schwann advanced the idea that all organisms are made of cells. • 1859 German biologist Rudolph Virchow stated that all cells divide

6. The light compound microscope The light compound microscope uses light to view specimens. It has two lenses. • Objective lens: is placed over the microscope slide containing the specimen. It collects light passing through the object and forms a magnified image of it. • Ocular lens (eyepiece): is placed at the top of the barrel. It collects the magnified image from the objective lens and further magnifies this image.

7. Electron microscope The electron microscope was developed in the 1930s and uses a beam of electrons instead of light as a source of energy. There are two types of electron microscope—the transmission microscope, transmits electrons through the specimen, and the scanning electron microscope in which bounces electrons off the specimen.

8. Cell Organelles An organelle is a small structure within a cell that performs a specific function. Each organelle has a structure that suits its function. Organelles are situated in the cytoplasm of cells and include: - Nucleus & nucleolus - Vacuoles - Mitochondria - Ribosomes - Endoplasmic reticulum - Golgi bodies - Lysosomes

9. Chemicals in Cells Chemical compounds in cells can be divided into two groups: • Organic substances: always contain carbon atoms. Examples include carbohydrates, lipids (fats), proteins and nucleic acids • Inorganic substances: may or may not contain carbon and are found in living and non-living things. Examples include water, salts, phosphates, carbon dioxide and metals such as potassium.

10. Volume Volume is the amount of space occupied by an object, expressed in cubic units. Volume = 2 x 2 x 2 = 8cm3 2cm 2cm 2cm

11. Surface area Surface area is the area of the outer surface of an object expressed in square units. SA = 6 x 2 x 2 = 24cm2 2cm 2cm 2cm

12. Surface area to volume ratio Surface are to volume ratio is the amount of surface area of an object compared with its volume. SA : V = 24 : 8 = 3 : 1 2cm 2cm 2cm

13. Surface area to volume ratio Substances move into and out of cells across the cell membrane. The cell membrane covers the surface of the cell and therefore has a surface area. The contents of the cell occupy a space or volume. The ratio of SA : V influences the rate at which substances can move into and out of the cell.

14. Surface are to volume ratio As objects become larger their SA : V ratio decreases. Cells are small because this keeps their SA : V ratio high. This in turn ensures that transport of substances across the surface area of the cell is fast enough to service the metabollic activities in the volume of the cell.

15. Cell membrane

16. Diffusion Diffusion is the movement of a substance from where it is more concentrated to where it is less concentrated.

17. Osmosis Osmosis is diffusion of water across a semi-permeable membrane from an area where it is at a greater concentration to an area where it is less.

18. Autotrophs and heterotrophs Plants are autotrophs which means they are able to make organic materials from inorganic materials. They do this by the process of photosynthesis. Other organisms, such as animals and fungi, that depend directly or indirectly on the organic compounds produced by producers are called heterotrophs.

19. Photosynthesis Photosynthesis can be described using a word equation: sunlight water + carbon oxygen + glucose dioxide

20. Plant structures & photosynthesis What structures ensure that plants have a ready supply of the materials needed for photosynthesis? Leaves • Flat shape provides a large surface area exposed to sunlight • Stomata provide access into the leaf for CO2 • Chloroplasts trap the energy of sunlight • Xylem and phloem vessels transport materials to and from the leaves

21. Plant structures & photosynthesis Stems • Xylem vessels give rigidity to stem and transport water and minerals from the roots to the rest of the plant • Branching of stems allows layers of leaves at different levels thereby increasing total area available for sunlight • Phloem transports products of photosynthesis via the stem to the rest of the plant

22. Plant structures & photosynthesis Roots • Tap water and minerals salts • Root hairs give a large surface area to volume ratio and this increases the area available for absorption of water and mineral salts. Leaves, stems and roots therefore combine to provide the sunlight energy, carbon dioxide and water that plants need for photosynthesis.

23. Mammalian Digestion In heterotrophic organisms the digestive system provides the means by which nutrients are taken in and broken down. Large insoluble food molecules are converted into small soluble ones that can be absorbed and made available to the body cells.

24. Mammalian teeth The function of teeth is to physically break down food into smaller pieces and so increase the surface area for enzyme activity (chemical breakdown). Humans have four types of teeth: incisors, canines, premolars and molars.

25. Mammalian teeth Incisors are flat sharp teeth for cutting and biting. On either side of the four incisors are two canines, which are adapted for ripping and tearing food. Premolars and molars are on either side of the canines and are used for grinding and crushing food.

26. Carnivore v’s herbivore

27. Exchange and transport in multicellular organisms Multicellular organisms need specialised systems to: • Obtain nutrients (digestive system) • Exchange gases with the external environment (respiratory system) • Distribute gases and nutrients to cells (circulatory system) • Remove cellular wastes (excretory system)

28. Gas exchange Gases exchange across the surface of cells all the time. Oxygen moves into cells and carbon dioxide moves out. Surfaces where gases enter and leave the body are called respiratory surfaces. Their characteristics include: • All living cells must be moist for gas exchange to occur. Oxygen and carbon dioxide are dissolved in water before they diffuse across respiratory surfaces

29. Gas exchange • Respiratory surfaces have a large surface area to maximise diffusion • Respiratory surfaces have a good blood supply to carry oxygen to body cells • Respiratory surfaces are thin so that gases can quickly move into the blood Different organisms have different strategies for exchanging gases.

30. Gas exchange in mammals Mammals have lungs. The respiratory surface of the alveoli, where most gas exchange occurs are protected within the body.

31. Alveoli

32. Gas exchange in frogs Most amphibians have soft moist skin with an extensive blood capillary network just below the surface. As a result gas exchange can occur directly through the skin. Most carbon dioxide is lost through the skin. A frog’s lungs consist of a pair of hollow sacs. Frogs first take air into a space behind the mouth called a buccal cavity.

33. Gas exchange in frogs This is separated from the lung by a glottis which opens and closes to control the movement of air into and out of the lung.

34. Gas exchange in fish Fish need to obtain their oxygen from water. Gills are the respiratory surfaces fish use for exchanging dissolved gases with the water around them.

35. Gas exchange in fish Gills are protected by bony plates and are constructed of many thin stacked layers that provide a large surface area for gas exchange. In addition, blood capillaries are just inside the surface of the gill tissue so that diffusion can occur efficiently.

36. Gas exchange in an insect Insects have a tracheal system where gases are transported to and from cells through a network of fine tubes (tracheae and tracheoles). These tubes are open to the air at the body surface. The openings are called spiracles.