Section 1 Introduction to Cells

1. Section 1Introduction to Cells

2. Animal Cell nucleus cytoplasm cell membrane

3. Plant Cell cell membrane nucleus vacuole cell wall cytoplasm green chloroplast

4. Nucleus • The nucleus contains the genetic material of an organism. • It controls all the cell’s chemical reactions. • It also controls the growth and development of a cell, and so determines the cell’s structure and function. nucleus

5. Cell membrane • Cells take in many chemicals from their surroundings, and release other chemicals into their surroundings. • The cell membrane is a very thin boundary which controls the entry and exit of these materials.

6. Cytoplasm • There are many chemical reactions happening in all of your cells. • These reactions keep the cell alive and allow it to carry out its specific function.

7. Cell wall • The cell wall is a rigid structure made of a tough mesh of cellulose fibres. • It helps to support a plant cell.

8. Vacuole • The vacuole is filled with water and pushes out towards the cell wall. • This provides support for the plant.

9. Chloroplasts • Plant cells may also contain chloroplasts in the cytoplasm. • These contain a chemical called chlorophyll which absorbs light energy for photosynthesis. • This allows plant cells to make food. • Only the green parts of a plant contain chloroplasts.

11. Microscopes • Cells are usually too small to be seen with the naked eye • Microscopes are used to magnify them • Stains (eg. methylene blue or iodine) can be applied to highlight certain cell structures • Your teacher will demonstrate how to prepare slides of onion cells and cheek cells, and you will then prepare your own slides and view them under the microscope. • You should make labelled drawings of what you see. Include the magnification used.

12. Examining Onion Cells • Equipment: • Glass slide • Cover slip • Onion skin • Iodine stain • Microscope • Lamp Aim: To observe and draw onion cells using a microscope.

13. Method: Collect a thin piece of onion skin. Spread the skin on a slide. The skin must not overlap. Stain the cells by adding 2 drops of iodine stain. Place a cover slip over the skin. Use a pencil to lower the cover slip gently so the air is pushed out. Examine the cells under low then medium power. You should be able to see lots of cells arranged like bricks in a wall. Adjust the microscope to a higher power. Draw exactly what you see through the “field of view” using a pencil. Label as many structures as you can see. Return the slide and pack your microscope away carefully.

14. Onion cells in iodine nucleus cell wall cytoplasm

15. Examining Cheek Cells • Equipment: • Glass slide • Cover slip • Cotton bud • Methylene blue stain • Microscope and lamp • Paper towel Aim: To make a slide of cheek cells and draw them.

16. Method: Rub the cotton bud over the inside of your cheek to remove some of the cells. Wipe the cotton bud over the surface of a glass slide. Place the cotton bud in disinfectant. Stain the cells with 1 drop of methylene blue stain. Remove some of the stain using paper towel. Use a pencil to lower the cover slip so the air is pushed out. Draw the cells and label the structures. Once you have finished, place the slide and cover slip in disinfectant. Pack away your microscope carefully.

17. Cheek cells in methylene blue nucleus cell membrane cytoplasm

18. Plant Cells • Some plant cells have chloroplasts. • These disc-like structures contain a green pigment called chlorophyll that traps light so that the plant can make its own food by a process called photosynthesis

19. cell wall chloroplasts

20. Comparison of Cell Types

21. Comparison of Cell Types

22. Textbook questions Answer q. 1-4 on page 4 in sentences

23. Multicellular Organisms Organisms are usually made up of millions of cells that work together e.g. oak tree or human These are called multicellular organisms

24. Unicellular Organisms But there are also organisms that are made up of just one single cell These are called unicellular organisms and are very small e.g. Amoeba

25. Different types of cells Microbes: a word used to describe a microscopic unicellular organism such as bacteria and fungi.

26. Microbes Some microbes are harmful and can cause disease. Others can be useful e.g. helping to make useful products in biotechnology industries. An example of a useful fungus is penicillium, which produces the chemical penicillin, an antibiotic.

27. Cells & Biotechnology • Yeast cells are important to biotechnology because under the right conditions they can convert sugars into alcohol and carbon dioxide – this process is called fermentation yeast sugar carbon dioxide and alcohol

28. Is a unicellular fungus. It cannot photosynthesise, it has no chloroplasts. It needs a food source e.g. sugar. It can respire anaerobically ( in the absence of oxygen). It is widely used in the brewingand baking industries. It reproduces by ‘budding’. Yeast cells can reproduce rapidly if they have a source of food and a suitable temperature. Yeast

29. 1 hour 30 mins 1 hour 30 mins 2 hours 2 hours 30 mins

30. Yeast dividing calculation • One yeast cell is placed in a sugar solution. It divides to form 2 cells in 30 minutes. How many yeast cells will there be after 12 hours? • How to work it out • 12 hours = 24 divisions • Number doubles each division

31. 2 • 4 • 8 • 16 • 32 • 64 • 128 • 256 • 512 • 1024 • 2048 • 4096 • 8192 • 16384 • 32768 • 65536 • 131072 • 262144 • 524288 • 1048576 • 2097152 • 4194304 • 8388608 • 16777216 Answer = 16,777,216 yeast cells

32. Looking at microbes • Yeast is a very useful microbe, it is a fungi. • Looking at yeast… Collect the following: • Microscope, slide, 1 drop of yeast, cover slip. • Prepare a yeast cell slide.  View the yeast cells at low and high power. Look for cells that are budding.

33. Looking at yeast cells

34. Applications of Fermentation by Yeast Brewing Industries Alternative Fuel Industries e.g. Gasohol (alcohol mixed with petrol) Bread-making Industries

35. Yeast and alcohol • Yeast can make alcohol when it has a source of sugar. • This is called alcoholic fermentation and is used in the brewing industries to make wine and beer.

36. Yeast and alternative fuels • Yeast can be added to sugar to make alcohol. • Alcohol is flammable and can be used as fuel. However, it must first be mixed with petrol. • This forms an alternative fuel called gasohol. alcohol (made by yeast) + petrol = gasohol

37. Yeast and breadmaking • Yeast is added to flour, water and a little sugar (to feed the yeast!). • The dough is then left for about and hour in a warm place. During this time the yeast produce carbon dioxide and a little alcohol. • The carbon dioxide gas causes the dough to rise. • It is then put in an oven to bake. This kills the yeast and evaporates off the alcohol.

38. Yeast and breadmaking • Label two beakers A and B. • Add 3 spoons of flour and half a spoon of sugar to each beaker. • Add yeast suspension to beaker A and mix with a stirring rod to make a dough. • Add water to beaker B and stir to form a dough. • Transfer the doughs to two measuring cylinders and transfer the labels A and B onto them. • Leave in a warm place for 30 minutes. • Look at the height of the dough in each cylinder.

39. Yeast and breadmaking Results Complete the results table. Conclusion: What effect does yeast have in breadmaking?

40. Antibiotic Production using other fungi Alexander Fleming Video clip

41. Antibiotic Production Antibiotics are antibacterial chemicals produced by microbes such as fungi. They prevent the growth and may cause the death of other microbes. Antibiotics do not work against viruses so cannot be used to treat the cold or the flu. Many bacteria are now resistant to antibiotics. Video clip

42. bacterial colony bacteria cannot grow near the Penicillium Penicillium colony

43. Antibiotic multidisc • A disc with several antibiotics on the ‘arms’ can be used to find out which is the most effective antibiotic to treat an illness. • This is used in labs where swabs from patients are sent for checking. Clear zone around arm shows that the bacteria is killed by the antibiotic. This would be a good antibiotic to give the patient.

44. Resistant bacteria In the above example, the bacteria M.Luteusis killed by antibiotic V. We say that the bacteria is sensitive to the antibiotic. In the above example, the bacteria S.Albus is not killed by the antibiotic V. We say that the bacteria is resistant to the antibiotic.

45. Resistant bacteria • If a bacteria is not killed by an antibiotic we say that the bacteria is resistant to the antibiotic. • If a bacteria is killed by an antibiotic we say that the bacteria is sensitive to the antibiotic. • An antibiotic multidisc can show which antibiotic is best to treat each bacteria.

46. The use of bacteria • Bacteria can be used to produce -Yoghurt -Biogas (another alternative fuel)

47. Yoghurt Making During the souring of milk, bacteria growing in the milk will feed on the milk sugar (lactose) and break it down to lactic acid. This process is called lactic acid fermentation bacteria Lactose Lactic Acid Lactic acid makes milk curdle. The manufacture of yoghurt depends on the curdling of milk

48. Investigating Microbes… • True or False… • Microbes are all harmful and can cause disease • Fungi can be used in yoghurt making • Bacteria can be killed by antibiotics • Yeast make their own food through the process of photosynthesis • Some bacteria are resistant to antibiotics • Fungi carry out fermentation • Fermentation releases oxygen • Yeast use glucose as an energy source for respiration • Gasohol is petrol mixed with alcohol • Antibiotics are produced by fungi

49. Diffusion • Diffusion is the movement of molecules in a liquid or gas from high to low concentration until they are evenly spread out Diffusion clip – BBC learning zone

50. Cells and diffusion • The entry and exit of substances in and out of cells is called diffusion. • This happens across the cell membrane. • Animal cells take in glucose and oxygen by diffusion. • Carbon dioxide and waste materials leave animal cells by diffusion.