S3 BIOLOGY UNIT 1: CELL BIOLOGY SUB-UNIT 1.3 PRODUCING NEW CELLS

Cell division In a unicellular organism (Amoeba) cell division is a form of reproduction which produces two new individuals. In a multicellular organism (human being or plant) cell division results in the growth of an organism. Cell division is the means of increasing the number of cells in an organism. It is the nucleus that controls cell division.

Cell division: Animal cell Nucleus divides Two daughter nuclei separate Cytoplasm pinches off Two daughter cells are formed.

Cell division: Plant cell Nuclear division Laying down of cell wall. Two daughter cells formed

Chromosomes Chromosomes are threadlike structures found in the nucleus. Chromosomes carry information necessary for the development of the cell and the survival of the organism. All body cells have a double set of chromosomes and are said to be diploid. One set of chromosomes come from the mother and the other set comes from the father.

Questions a)State the main events that occur during cell division. b)How does cell division in a plant differ from that in an animal? c)Which cell structure controls all cell activities including cell division? d) Draw a diagram to show genes on a pair of chromosomes:

Video time TWIG video clip : Cell division: Mitosis BBC - Learning Zone Class Clips - Mitosis - Science VideoBBC - Learning Zone Class Clips - Mitosis - Science Video

Mitosis Mitosis is the process of cell division where the nucleus divides into two daughter nuclei. Each nuclei has exactly the same number of chromosomes as the original nucleus.

Stages of Mitosis

1.Chromosomes become shorter and thicker (like a double thread). 2.Each single thread is called a chromatid. 3.The two chromatids are joined by a centromere. 4.Chromosomes line up at the equator. 5.Spindle fibres attach to the centromere of each chromosome. 6.The centromere splits and one chromatid moves to the “north” pole and the other to the “south” pole. 7.Finally a nuclear membrane forms around each group of chromatids (now called chromosomes). Nuclear division (mitosis) is complete forming 2 new daughter cells which are identical.

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Chromosome complement Every species has a definite and characteristic number of chromosomes present in each cell, this is called the chromosome complement. Since chromosomes provide the genetic information for each species, it is essential that each new cell receives a full complement of chromosomes. This ensures that animals and plants are provided with all the characteristics of their species.

SpeciesDiploid chromosome complement Onion 16 Rice 24 Fruit-fly 8 Cat 38 Human 46

Questions a)Describe the process of mitosis in a cell including the terms chromatid; centromere and spindle fibre in your answer. b)Why is it important that the chromosome complement of daughter cells in a multicellular organism is maintained?

Cancer What?Who?Types?

Causes of cancer (case studies) Read the case studies and complete the table. Think about –How old the person was when they developed cancer –What you think the possible causes are

Causes of cancer (case studies) POSSIBLE CAUSES

Causes of cancer (case studies) POSSIBLE CAUSES Richard 70 Emily 35 Peter 69 Myra 74 Daniel 65 Kate 35 smoking Old age Viral infection HPV sun Old age unknown Old age Unhealthy diet Old age Lack of exercise inherited

Causes of cancer (case studies)

Most of the case studies developed cancer over the age of 65. There are preventable and non- preventable causes. Only a small proportion (5%) are attributable to an inherited gene defect.

Look at case study 5, you will see that there isn’t always a clear cause. A healthy lifestyle can reduce your chances… but there are no guarantees.

PreventableNon-preventable SmokingInherited Unhealthy dietAge Lack of exerciseUnknown (biological processes) Overexposure to the sun Infection with a virus (e.g. HPV)

How does cancer develop?

The Road to Cancer

Key concepts Cancer is a disease of cells. Cancer develops when cell division (mitosis) goes out of control. Cancer is a disease of old age.

Quiz answers

Working with Micro-organisms There are micro-organisms all around us. It has been estimated different species of bacteria live on human skin. The experiment on the right investigates micro-organisms in the air. Each plate has a layer of nutrient agar. Any microbe that lands on this agar will grow and multiply because they can feed on the agar. Plate A was exposed to air for 30 minutes. Two days later bacteria and fungi had grown. Plate B was not exposed to air and no bacteria or fungi grew. Why did microbes grow on plate A and not plate B?

Aseptic technique Before learning about aseptic technique you should be familiar with a few terms. Watch the video and try to write down the meanings of the following words: Video: Working with cells | Wellcome Trust

WORDMEANING MEDIUM STERILE MEDIUM CULTURE PURE CULTURE MIXED CULTURE CONTAMINATION DISINFECTANT INNOCULUM Cell food Cell food that is free from any bacteria or living organisms The growing micro-organisms in a nutrient rich environment A sample of only one type of micro-organisms growing in a nutrient rich environment A sample of more than one type of micro-organism growing in a nutrient rich environment The accidental introduction of foreign micro- organisms to a culture sample. A chemical used to eliminate foreign micro-organisms from the working area. A solution containing micro-organisms that is added to a sterile, nutrient rich environment for observation.

Precautions and sterile technique In a microbiology laboratory it is important to take precautions when working with micro-organisms. All surface should be made of plastic and be sterile (have no microbes living on them). These microbes can be killed with disinfectant. Microbiologists working in the lab need to wear lab coats to protect their clothing and be careful not to touch the agar used to grow microbes. All glassware also must be sterilised. It is heated in an autoclave at 121 o C for 20 minutes to ensure all microbes are dead – some can survive in boiling water!

Culturing a microorganism In microbiology, Scientists grow micro- organisms. They grow bacterial “cultures” on agar plates. The diagram shows the method used to inoculate (introduce) a fungus to the petri dish.

Resistant spores All these precautions are taken so that the only microbe growing in the agar plate is the one the microbiologist is trying to grow. If these steps were not taken the wrong microbe may be grown. The reason high temperatures of autoclaves and Bunsen burners are used is to kill resistant spores. Some bacterial cells can become endospores. This means they produce a thick protective coat. Fungi can do likewise. Only exposure to temperatures above 120 o C applied under pressure can kill these resistant spores.

Questions a)Why should a microbiologist wear a lab coat? b) What is used to clean all surfaces before working with microbes? c) Why are these precautions taken? d) How are resistant spores killed? Protect clothing Disinfectant Reduce risk of contamination Expose to temperatures over 120 o C

Cell culture: treatment of burns Watch the video and then write a short report on the use of cell culture in the treatment of burns. BBC - Learning Zone Class Clips - Growing new skin cells - Science VideoBBC - Learning Zone Class Clips - Growing new skin cells - Science Video

Fermenters Biotechnological industries grow micro-organisms on a vast scale to make vast quantities of useful products (e.g. _______________). Industrial fermenters are used to make these antibiotics, enzymes and vaccines. The industrial fermenters are automated. This means they are automatically controlled by computers. Sensors monitor the conditions for growth and make sure they are right for the product they are making. The computers may monitor : Temperature Oxygen concentration pH Glucose concentration alcohol

The diagram below shows a fermenter that is making a fungus.