chromosomes duplicate B5 Growth and Development – B5.1 How does an organism produce new cells? 2.Mitosis: Cell division by mitosis produces (four / two) new cells (different / identical) to each other and to the parent cell. Before mitosis can occur there must be a cell (growth / reduction) phase when the numbers of organelles in the (cytoplasm / nucleus) increase and the chromosomes in the (cytoplasm / nucleus) are copied by (four / two) new strands of DNA form alongside them. Mitosis occurs when the copies of the chromosomes separate and the cell divides into (four / two). 1.Why does an organism produce new cells? All organisms must produce new _______ to grow, repair damage and to reproduce. All cells start their lives with a __________ that contains __________ , which are made from long molecules of ______ . The DNA has a _______ helix structure that allows it to make exact ______ of itself and provides instructions ( ________ ) so that the cell can make the right ________ at the right time. 1 2 3 4 5 6 7 New nuclear membranes begin to reform around the two new nuclei. The chromosome pairs separate and move to opposite ends of the cell. chromosome DNA double helix The two identical daughter cells separate from each other. The DNA becomes shorter and fatter allowing the chromosomes to be seen. Chromosome pairs line up along the centre of the cell. The nuclear membrane breaks down so the chromosome pairs can move around the cell. Word bank: single, proteins, DNA, genes, copies, nucleus, double, chromosomes, cells 1 The parent cell containing DNA spread out in the nucleus. 3.Mitosis: 4.Sexual reproduction and meiosis: Most plants and animals reproduce ____________ . Male and female sex cells or ___________ join up at ___________. A fertilized egg is called a ________, which divides to produce the new organism. The zygote contains a set of ____________ from each parent. The zygote contains instructions for making all the different types of cells in the organism’s body. Word bank: zygote, asexually, gametes, chromosomes, sexually, fertilization Gametes contain only half the number of chromosomes compared to body cells. They are produced by a special type of cell division called Meiosis. It is important that the cells produced only contain half the chromosome number of the parent cell. Complete the diagram of Meiosis by adding the right number of chromosomes to the empty dividing cells. Meiosis (MEI) or Mitosis (MIT)? 1. How many cells above are in the mitotic phase? …....... 2 cells produced parent cell 2. How many cells above are in the growth phase? ……..… 4 cells produced chromosomes duplicate 3. Why must cells divide? ………………………………………………………………………………...………..........………………………………………………………………………………………………... New cells are identical to the parent cell first division MIT New cells are used for growth 4. What two steps happen during cell growth? ……………….. …………………………………………………………………………………………………….. second division New cells contain half the number of chromosomes compared to the parent cell. 5. How many cells are made from one parent cell by mitosis? ………………………………………………………………………………..….. gametes

B5 Growth and Development – B5 B5 Growth and Development – B5.2 How do genes control growth and development within the cell? 5.DNA structure and replication: (1) Base pairing means exact copies of DNA can be made. (2) Weak bonds between bases split, opening up the DNA from one end to form 2 strands. Immediately, new strands form from free bases in the cell. (3) The two new chains are identical to the original because A always pairs with T, and G always pairs with C. Both strands of the DNA molecule are made up of 4 different bases, which always pair up the same way. This is called base pairing. Fill in the correct base pairs (A,C,G,T) T Features are passed on from parents to their offspring because information is carried on the chromosomes. Chromosomes consist of DNA, which has a double helix structure (a bit like a twisted ladder). chromosome DNA double helix pairs of bases between two chains chains made of deoxyribose (a type of sugar) and phosphates (1) (2) (3) Fill in the correct base pairs (A,C,G,T) 6.Making proteins The genetic code is in the nucleus but proteins are produced in the cell cytoplasm. Genes do not leave the nucleus but a copy of the gene, messenger RNA (mRNA), is produced to carry the genetic code to the cytoplasm. 1. The bases in a DNA molecule always bond in the same way (4,7) 2. The small molecules that make up proteins (5,5) 3. The division that produces gametes (7) 4. Sex cells (7) 5 A. Messenger RNA (4) 6. A sequence of 3 bases coding for a particular amino acid in the genetic code (7,4) 5 D. The division that produces cells for growth (7) 1. 2. 3. 4. 5. 6. The order of the bases in a gene is the code for building up amino acids in the correct order to make a particular protein. Word bank: nucleus, gene copy is made; amino acids; different; cytoplasm; 3 DNA bases; amino acids are joined together; gene copy leaves the nucleus;

What are these specialised cells? B5 Growth and Development - B5.3 How do new organisms develop from a single cell? 7. Making a new human Finish the sentences What are these specialised cells? You began your life as a single cell but now you are made of millions of cells. Your development has been gradual. The heart and brain in humans are ….. tissues Humans have more than 300 different types of cells, they are ……. Zygote (Egg cell fertilized by a sperm cell) Zygote divides to develops into a ball of cells. This is called the embryo. specialized Cells that have particular functions are ….. organs Groups of specialised cells are called ….. Zygotes divide by (mitosis / meiosis) to form an embryo. In a human embryo, up to the (4 / 8) cell stage, all the cells are (different / identical) and could produce any sort of cell required by the organism. These are called embryonic stem cells. After this point the cells become (specialised / unspecialised) and form (the same / different) types of tissue. organs Groups of tissues are called ….. multicellular Specialised cells – special proteins Your body has more than 300 types of cells. Each cell type has its own set of proteins. Keratin is a structural protein found in hair, skin and nails and it is strong and insoluble. Stem cells Adult and embryonic stem cells have the potential to produce cells needed to replace damaged tissues. In carefully controlled conditions of mammalian cloning, it is possible to reactivate inactive genes in the nucleus of a body cell to form cells of all tissue types. Nerve cells Heart muscle cells Insulin secreting cells Skin cells Burns and ulcers Diabetes Parkinson’s disease Damage caused by heart attack Although body cells in an organism contain the same genes, many genes in a particular cell are not active because it only produces the specific proteins it needs. Genetic switches are used to switch genes on and off. In the chromosomes above, which would you find in an unspecialised cell? ( ) Are the genes involved in respiration turned on or off in all cells? ( ) Does turning genes off make a cell specialised or unspecialised? ( ) What do genes give the codes to make? ( )

B5 Growth and Development - B5 B5 Growth and Development - B5.3 How do new organisms develop from a single cell? 8. Plant development: Unlike animal cells some plant cells remain unspecialised and can develop into any type of plant cell Plant meristems divide to produce cells that result in increased height length of roots and girth of plant Unlike animals, most plants continue to grow in height and width throughout their lives. New cells in plants specialise into cells of roots, leaves or flowers Unspecialised cells produce clones of a plant. You can make from cuttings. If the hormonal conditions in their environment are changed, unspecialised plant cells can develop into a range of other tissues or organs Explain the diagram above.