B5 Growth and development. B5 Growth and development. Question How many different bases are found in DNA?

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1 Q1 How many different bases are found in DNA? Q2 Which DNA bases always pair together? 4 A with T G with C Q3 What is a gene? Q4 What are proteins made of? A gene is a short section of DNA that contains the instructions for a protein. Amino acids

2 Q5 Describe how the order of bases in a gene determines what protein is made. Q6 Where in the cell are genes found? The order of bases is the genetic code. Each set of 3 bases codes for one amino acid. The order of the bases tells the cell what order to put the amino acids in. The nucleus. Q7 Where in the cell are proteins made? They are made in the cytoplasm (by ribosomes). Q8 Why is a RNA copy (messenger RNA) of the DNA made before proteins are produced? DNA is too large to move out of the nucleus. To get the information from the DNA to the ribosome, a copy of the DNA is made using mrna. mrna is similar to DNA but is shorter and single-stranded.

3 Q9 During cell growth does the number of chromosomes double or halve? It doubles. Q10 Which type of cell division is used to provide new cells for growth and repair? Mitosis Q11 Which type of cell division is used to create gametes (sex cells)? Meiosis Q12 In which type of cell division are the cells produced identical? Mitosis

4 Q13 Which type of cell division produces cells with half the number of chromosomes compared to the parent cell? Meiosis Q14 What is the name of the cell produced when two gametes combine? Zygote Q15 Q16 In a human embryo, all the cells are unspecialised until what stage? 8 cell stage How are embryonic stem cells different to adult stem cells? Embryonic stem cells have the ability to become any type of specialised cell. Adult stem cells can only differentiate into certain types of cell.

5 Q17 What determines the type of cell that a stem cell becomes? It depends upon which genes are active. In specialised cells most of the genes are not active, this means that the cell only produces the specific proteins that it needs. Q18 How could cloning be used to make embryonic stem cells? Remove the nucleus from an egg cell and replace it with one from an adult body cell. Under the right conditions, inactive genes can be reactivated so that an embryo forms. Embryonic stem cells can be removed from the embryo. Q19 What name is given to the parts of plants where mitotically active cells are found? Meristems. Q20 Name two types of tissues that the unspecialised cells in plants can turn into. Xylem Phloem (any other plant tissue)

6 Q21 What is a cutting? Q22 What do cuttings grow into? A part of a plant that has been cut off. A whole new plant can be grown, it will be a clone of the parent plant. Q23 What can be added to cuttings to encourage roots to grow? Rooting powder. It contains plant hormones (auxins). Q24 What is phototropism? Give examples of negative and positive phototropism. Phototropism is how a plant responds to light by growing in a certain direction. Negative phototropism grow away from the light e.g. roots. Positive phototropism grow towards the light e.g. shoots.

7 Q25 What name is given to the process of stem cells becoming specialised? Differentiation. Q26 Why is it possible to use bone marrow transplants to treat people with blood diseases? Bone marrow contains stem cells that can turn into new blood cells to replace the faulty ones. Q27 Embryonic stem cells have huge potential for treating a wide range of illnesses. Why do some people think it is unethical? The embryos used to create the stem cells are destroyed and they could have become a person. Q28 What are auxins and what do they do? Auxins are plant hormones that control growth near the tips of shoots and roots. Auxins are produced in the tip and diffuse backwards. They cause cells to elongate and grow.

8 Q29 Are shoots negatively or positively phototropic? Why? Shoots are positively phototropic. They need sunlight to carry out photosynthesis, hence they grow towards light. Q30 Explain how auxins cause plant shoots to grow towards the light. When a shoot tip is exposed to light, more auxins collect on the side that is in the shade. The cells on this side elongate faster and so the shoot grows towards the light. Q31 What experimental evidence was used to demonstrate the effects of auxins? If you remove the tip from a shoot then it does not grow (no auxins). If you cover a tip in foil and shine a light from one side then it will grow straight up as the auxins have an even distribution.