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Biology 12.

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Presentation on theme: "Biology 12."— Presentation transcript:

1 Biology 12

2 Cell division Needed for: reproduction in unicellular organisms
growth in multicellular organisms replacement of damaged or dying cells repair of damaged organs or tissues

3 Mitosis Involves: replication of DNA
controlled division of the nuclear material so new each cell has the same DNA division of cytoplasm and organelles so each new cell has similar contents

4 DNA replication Occurs in interphase – before mitosis starts
One set of enzymes split the strands Another set of enzymes join new nucleotides to each strand Nucleotides match up by the base pairing rule (C – G, A - T) The end result is two identical strands, joined at a point called the centromere

5 DNA replication 2

6 Chromosomes Chromosomes are only visible during cell division
They consist of two strands (chromatids) of tightly coiled DNA joined at the centromere

7 Cell cycle

8 Stages of mitosis

9 Interphase Phase of growth and normal metabolism
Nucleus and nucleolus visible DNA replication occurs just before cell division occurs

10 Prophase First stage of division Nucleus and nucleolus disappear
Spindle starts to form DNA condenses and becomes visible as chromosomes Centrioles move to opposite poles (animal cells)

11 Metaphase Chromosomes line up on spindle at the equator of the cell

12 Anaphase Chromatids pull apart at the centromere
One chromatid from each chromosome moves to each end of the cell

13 Telophase Chromosomes uncondense and a new nucleus forms around them
The cytoplasm splits (cytokinesis) to form two new cells identical to the original except smaller

14 Interphase Phase of growth and normal metabolism
Nucleus and nucleolus visible

15 Identify the stages of mitosis
telophase anaphase interphase metaphase early prophase early prophase metaphase early prophase

16 Identify the stages of mitosis 2
telophase late anaphase/early telophase anaphase prophase early prophase late anaphase/early telophase metaphase interphase

17 Designing experiments
Pose a question Suggest some answers Define your hypothesis eg using pesticides will increase yield

18 What shall I change? Select one thing to test
That is the independent variable eg pesticides

19 How do I know if it has an effect?
eg yield Measured by weight, height or volume What will I measure? How will I measure it? That is the dependent variable What will I compare it to? That is the control eg group without pesticides

20 How do I know my results are true?
Define your controlled variables Define how you will increase reliability eg same soil type, same type & number of seeds/plants, same water, sun, temperature, humidity, weed control, fertiliser, etc

21 The language of experimental design
Hypothesis Independent variable Dependent variable The control Controlled variables Reliability

22 Ways to increase reliability
Use accurate measurements Increase number of measurements Run experiment for longer Repeat the experiment Increase the sample size Get someone else to replicate the experiment Share the results and get a review

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