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Transcript
Cell division and Survival Reproduction of cells is essential if an organism is going to grow, repair itself and replace cells that have died. As far as the species is concerned it is even more essential that the organism replaces itself with a younger replacement. 1. Cells of Producers (plants) and Consumers (animals) are similar in many respects. Label the organelles in the two types of cells below and answer the questions that follow. green c___________________ c______ w_______ cy____________ m________________ n_________ containing ch____________ _ large v__________ __ c_____ m__________ What are the three organelles plant cells have, that animal cells do not? i)_____________________ ii)__________________________ iii)______________________ 2. Fill in the gaps in the following sentences explaining where genes are and cell division by Mitosis. The n____________ is the control centre of the c_______. It contains ch______________ which carry on them all the instructions for how to make the complete organism. The instructions are written in a code as A single gene on a length of chromosome ( a bit of DNA) individual g_________. There are actually two sets of instructions (two sets of c______________) in every cell in an organism (two sets of g________). One set came from the m_______ parent and one set came from the f________ parent. All organisms start off with a single cell that divides again and again to grow a complete individual. Single cell with two sets of chromosomes in its nucleus Both sets of ch____________ need to be co___________ exactly into every n_____ c___ or the cells would not know how to do what they were supposed to do. The process of making an exact c__________ of a cell is called M_______. Two identical cells are made from one cell and genetic material (the ch___________ and the g___________ that make them up) are exactly the same as the single cell that d_________ by M_________ Two identical cells produced by Mitosis cell division Asexual Reproduction –reproduction without sex Because every cell in an organism contains a complete set of genetic instructions on how to make the entire organism you can grow one exactly the same from a single cell (this is called cloning). However it is easier to do it from a whole group of cells. Because you are reproducing a new organism without sex it is called asexual reproduction. Plants and some animals (aphids) naturally reproduce asexually. 1. Label the following diagrams of plants that naturally use asexual reproduction to colonise an area of ground. Clover Plants Twitch grass Potato plants Pa_________ plant St_______ above ground Pa_________ plant identical cl_____ of plant Rh______ below ground Pa_________ plant identical cl_____ of plant T_______ identical cl_____ of plant 2. Man also uses the method of asexual reproduction to mass produce plants which grow up identical to their parents. They are the same plant simply growing on a different set of roots. Label the following diagrams and complete the sentences below showing how cuttings are made. Axial Bud A branch of a plant that is required to be a______________ r_____________ is chosen and a small length is cut off that contains a growing m___________, an ax________ bud and a couple of le______. The c__________ has exactly the same g________ in every cell’s n___________ as the parent plant it was taken from. It will grow up looking exactly the same because it is a c_________. The cutting must make ad_______________ r___________ on its stem if it is going to suck up water and minerals to survive. It is placed carefully in damp sand to allow for these roots to develop. The c___________ has a plastic bag over the whole pot to prevent the cutting losing too much water before it has grown it’s a________________ r_________ and is able to survive as a separate new identical c________ of the parent plant. Advantages and Disadvantages of Asexual Reproduction 1. Examine the drawing above and complete the following sentence. Because all c__________ have exactly the same g_________ on their ch_____________ the major disadvantage of a_______________ r is that any disease or climatic event that kills one individual will kill them all. 2. Examine the drawing above and complete the following sentence. If the individuals do not have the same g_________ on their ch_______________ some will survive to reproduce and the species will carry on in a modified way. This is the basis of Evolution – selection by survival of the fittest. 3. Natural and artificial asexual reproduction is not all bad. There are significant advantages as well. The top line of trees were all produced using asexual reproduction by growing cuttings. As a forest grown for logs and timber, state two advantages and one disadvantage these trees would have over the bottom row which were not genetically identical.(seed grown) Ai)______________________ ________________________ Aii)______________________ ________________________ Di)_______________________ ________________________ 4. Complete the following sentence to revise the other major advantages of asexual reproduction. If the growing season is shortened by a long winter, or if there are no pollinating insects, if there is only a single individual left, it cant do sexual r______________ The The individual can still do a___________ r___________ and the species su_____________ for another year and colonises the area of ground, keeping out competing plants. Sexual Reproduction using Meiosis Sexual reproduction produces a new individual that is different from its parents. Every cell has two sets of chromosomes (Diploid 2n). One set came from the female parent and one set came from the male parent. The single sets have to be packaged in a single cell as a gamete (Haploid n ). Meiosis is the cell division that enables these packages (gametes) containing a single set of chromosomes to be made from cells that contain two complete sets of chromosomes. 1. Complete the following sentences that explain the diagram on the right. 2n 2n The female body cell has two complete sets of two ch______________. It is a d_________ cell (2n) because it contains two sets of two chromosomes. n n n n One set came from her m___________ and one set n came from her f_________. Organisms have different n numbers of ch__________ that make up a complete set. Humans have two sets of 23 ch_____________. n for humans is therefore 23. Every d____________ cell in a human has 46 ch_____________. Gorillas have two sets of 24 chromosomes (n= 24) so every gorilla body cell has 48 chromosomes. The diploid cell d_________ by M_________ to form g___________ that contain only o______ set of ch_____________. These are called h___________( n) cells. Notice that the female gamete in this case has o________ set of two chromosomes. The same M__________ cell division occurs in the male d_________ cell. The male cell produces h___________ g___________ that contain only one set of ch______________. The two gametes fuse together in a process called f__________________. This results in a cell called a z__________. The z__________ contains the required two sets of c_______________ and is d_____________. This cell then divides by mitosis and a new genetically different individual grows. The start of a new life! Gametes form in the ovaries of women and the testicles of men. Single celled Zygote formed from fertilisation 2n Answer the following questions about the diagram above. 2. How many complete sets of chromosomes did each parent have? ___________ 3. How many complete sets of chromosomes do the gametes have? ___________ 4. How many complete sets of chromosomes does the fertilised zygote have? ___________ 5. How many chromosomes make up one set in this species of cell? 6. What is the n number in the cells above? ___________ 7. n is 23 in humans . How many individual chromosomes are there in every body cell? _____ 8. How many individual chromosomes are there in each gamete? ___________ 9. How many individual chromosomes are there in a fertilised zygote? _________ Mendelian Genetics and Punnett Squares All body cells are diploid (have two complete sets of chromosomes). They therefore contain two genes (two sets of instructions) for everything the organism looks like and does. All gametes are haploid because they only contain one set of chromosomes. The gametes therefore must contain only one complete set of genes each. When gametes from two different parents fuse by fertilisation the zygote again becomes diploid and has two sets of instructions (genes). A punnett square is a simple device to look at the likely outcomes from a mating of two different individuals. The genes are given single letters and there are always two letters (signifying diploid) given for each parent e.g. TT, Tt or tt. Female parent T = Dominant gene = Tall t = Recessive gene = short Tall Gametes Gametes Male parent Tt T t T TT Tt Phenotype t Tt tt Genotype Offspring Tt Tall ¾ tall ¼ small ¼ TT ½ Tt ¼ tt 1. Complete the table linking the scientific term with its correct definition (arrow) and write in the letter, letters or words from the diagram above that correspond with the definition (one has been done for you). Scientific Term Definition Dominant gene is two letter shorthand for the combination of Genes in every cell of the organism the zygote grows into. The dominant gene is always written first. is written with a capital letter and as the name suggests is the set of instructions the zygote cell uses to make something look the way it does Recessive gene Phenotype Genotype Homozygous Heterozygous Gamete is when both the genes in every cells nucleus are the same. (Hint think homosexual = likes the same sex) is a fertilised egg (the first diploid cell made when two gametes fuse ). is written with a small letter. This gene will never be used as a set of instructions to change its looks unless the zygote cell has no alternative. The cell produced by meiosis that is haploid (contains only one set of chromosomes) eg sperm, egg, ovule, pollen. is the Physical expression of the gene (what the zygote looks like when it has grown up). Letter, letters or words __ __ __ _ TT tt __ __ __ __ _ _ ______ Zygote is when both the genes in every cells nucleus are different. (Hint think heterosexual = likes the different sex) __ Punnett Square practice 1. Complete the following sentences. These two plants are both peas. They look Physically different because the P______________ of the one on the left is short and the p______________ of the one on the right is tall. The tall p________________ plant must have at least one d__________ gene in its g_____________. It would therefore be either T t or _ _. The tall plant therefore can be either Tt which is called h______________ or TT called h_____________ d______________. The short _______________ plant can not have a dominant gene in it so it must have a g_____________ of _ _. This genotype is called ho_________________ r__________________. Gametes 2. If these two plants are crossed the gametes they produce will be transferred as pollen and fertilise the ovules of the other plant. The zygote that develops from the fertilised ovule grows into a seed that would then grow into an offspring pea plant. Complete the Punnett squares below and predict both the fraction split for genotype and phenotype as was done on the previous page. a) Female TT Tall parent T = Dominant gene = Tall Gametes t = Recessive gene = short T T Offspring T Male parent Phenotype all _____ ___ Short Genotype ½ TT ___ _____ Tt t Tall b) Female parent T = Dominant gene = Tall t = Recessive gene = short Tt Tall Gametes Gametes Offspring Phenotype Male parent Short tt Genotype ___ _____ ___ _____ ___ _____ ___ _____ ___ _____ Sex determination in Humans The sex of a zygote, that grows into a baby and then into one of us, is determined not by a single gene on a chromosome but by the length difference of an entire pair of chromosomes The sex chromosomes are called X and Y. Hint Looking at the letters Y is simply an X that has lost a bit. The Y chromosome has lost a bit and is shorter than the X chromosome) XX zygote cells are female. One of the X chromosomes still came from the mother of the girl zygote and the other X chromosome came from her dad. XY zygote cells are male. The X chromosomes came from the mother of the boy zygote and the Y chromosome came from his dad. The sex of a baby is therefore determined by which sperm gamete wins the race. One containing a short Y chromosome will fertilise the egg and make the zygote a boy. If a sperm gamete wins that contains the longer X chromosome a girl zygote will be made. XX From their Mum XY From their Dad 1.Complete the Punnet Square below for sex determination in humans. and fill in the Offspring table showing fractions as usual. Female parent gametes X = long chromosome = female Y = short chromosome = male XX tall gametes Offspring Phenotype ___ _____ ___ _____ genotype ___ _____ short ___ _____ ___ _____ We all know there is a girl out there just waiting for us (and a boy if you are a girl) and the Punnet Square predicts that half the babies born will be female XX and half XY. Male parent XY The Punnet Square Offspring box therefore predicts the proportions of likely numbers of different phenotypes that will occur in a population. eg 50% male : 50% female. 2. Complete the following sentences. The major advantage in s_______ reproduction by m___________ is that there is va__________ in p________________ ( what the offspring look like) and g______________ (what their two sets of g_______ are). Because they are dif_________ from their parents that d___________ may allow that individual a comparative advantage so it has a greater chance of r___________ and passing on its g___________ to its offspring. In the picture below the white flowers were all killed which left the dark flowers to breed and the dark coloured flowers took over. Evolution- survival of the fittest works in this way. 3. Write a short statement about what happened to the mouse population. _________________________ _________________________ _________________________ _________________________ _________________________