Mitosis and Meiosis

Science Interactive LTD Multimedia CD-ROM for PC is a collection of 38 units totalling over 1150 PowerPoint slides matched to current single and double Science GCSE syllabuses. Each unit covers a wide range of different delivery and learning styles, offering an exciting way to involve your pupils during lessons or revision sessions. All styles of teaching and learning are supported through use of high quality images, graphics, challenging exercises and questions. Units can be used in the classroom via an interactive whiteboard , data projector or used during individual study via a PC or school network. Full users’ licence is available under our ‘ comprehensive package ’ or lessons can be purchased separately. Science Interactive LTD. PO BOX 50764 LONDON NW6 9AT email: sales@science-interactive.co.uk web: www:science-interactive.co.uk GCSE SCIENCE OCR EDEXCEL AQA Science Interactive LTD Copyright 2005 Unit 19: The Transitional Metals Unit 18: Metals and their Properties Unit 17: The Alkali Metals Unit 16: The Periodic Table and its Elements Unit 15: Genetic Engineering Unit 14: Evolution and Human Impact Unit 13: Inheritance and Selection Unit 12: Mitosis and Meiosis Unit 11: Flow of Energy and Elements through the Environment Unit 10: Water Transport in Plants Unit 9: Photosynthesis in Green Plants Unit 8: Drugs and Bad Body Maintenance Unit 7: Hormones and the Endocrine System Unit 6: Human Homeostasis Unit 5: Nervous System and the Senses Unit 4: The Respiratory System Unit 3: Healthy Body and Immunity Unit 2: The Circulatory System Unit 1: The Digestive System Unit 38: Cells, Tissue, Organs and Organs systems Unit 37: Natural Forces Unit 36: Sound and Hearing Unit 35: The Alkaline Earth Metals Unit 34: The Earth and Plate Tectonics Unit 33: Earth and Space Unit 32: Newton's Forces and the Effects of Forces Unit 31: Radioactivity Unit 30: Light and the Electromagnetic Spectrum Unit 29: Electricity Unit 28: Generating Electricity and its Domestic Use Unit 27: Energy Unit 26: Rates of Reaction Unit 25: The Noble Gases, their Properties and Uses Unit 24: The Halogens, their Uses and Compounds Unit 23: Ionic and Covalent Compounds Unit 22: Elements, Molecules and Compounds Unit 21: Rock Cycle Unit 20: Crude Oil and its Products

Unit 12

Mitosis and Meiosis

That lost or damaged cells need to replaced in the human body by mitosis.

That mitosis is how organisms like humans grow during pregnancy, through puberty to adult life.

That meiosis in humans leads to the production of the sperm and egg cells.

That during meiosis, the number of chromosomes in both the sperm and the egg cells are halved.

That during meiosis, random crossing of paternal and maternal DNA takes place producing genetically unique sperm and ovum.

That this random crossing during meiosis leads to variation in both the genotype and phenotype of humans.

How the sex of an individual is determined by the chromosomes we inherit from our parents.

Inheritance, Genes, Chromosomes, Alleles, Mitosis, Meiosis, Sperm, Ovum, Cells, Division, Clones, Reductive, Traits, Gametes, Variation, Characteristics, Recessive, Dominant, Genetic, Crosses, Diploid & Haploid. Unit 12: Mitosis and Meiosis web: www.science-interactive.co.uk email: sales@science-interactive.co.uk Science Interactive LTD PO BOX 50764 LONDON NW6 9AT Click mouse to begin Science Interactive LTD Copyright 2005 Understand: Keywords:

Numbers of cells Cells are the building blocks of all life. Unlike simple bacteria and other unicellular organisms, living organisms contain from many millions to billions of cells. Cells can have a very wide range of f___________ in the human body from skin cells, blood cells, muscle cells to nerve cells. Cells can only be viewed using a light microscope. Robert Hook was the first scientist to observe plant and animal cells using a simple light m___________ over 300 years ago. List the cell types that you have observed under a light microscope ? Numbers of cells in living organisms: Science Interactive LTD Copyright 2005 Word bank: functions microscope A small mammal, for example a rat contains many millions of cells organised into nine distinct organ system similar to our own. List these organ systems ? Small mammal A human contains many billions of cells. Each hour of every day of our lives, we replace over one billion cells in our body. During puberty we produce even more cells. A typical insect like a fly or a bee contains many hundreds of thousands of cells. Insects have very basic organ systems that support life and allow insects to reproduce. A bacteria is a simple single celled organism. All the bacteria found on the surface of this planet weigh more than any other species. They are very successful. Notes Diagram Organism Bacteria Insect Human

Essential cell organelles Cell organelles, like mitochondria and chloroplasts carry out important functions in plant and animal cells. The n_________ controls the activity of the cell by building new proteins including enzymes. It also contains DNA, the material of inheritance and is able to divide and produce new daughter cells during cell division or mitosis. Mitochondria found in both plant and animal cells respire glucose with o__________ releasing cellular e_________, carbon dioxide and water. Chloroplasts found only in plant cells produce glucose and oxygen from carbon dioxide and water ! Cell organelles in plants and animals: Science Interactive LTD Copyright 2005 Word bank: nucleus oxygen energy The cell’s nucleus contains the necessary genetic information or genes to produce new cells, new enzymes and new proteins. Humans have over 31,000 genes. Nucleus The cell membrane controls the passage of substances in and out of the cell. Movement of molecules happens by passive diffusion or active uptake. Found only in plant cells, chloroplast are able to combine carbon dioxide and water using the energy from light to produce glucose and oxygen. Mitochondria are found in both plant and animal cells. They respire glucose with oxygen to release energy for cellular activities. They release CO 2 and water. Function Diagram Organelle Mitochondria Chloroplast Cell membrane

Specialised cells in animals Cells are designed for the specific function they play in the human body as part of the billions of cells that work to together to support life. A nerve cell for example is long and t_____ and conducts e__________ impulses. A red blood cell has a large surface area and no n________ so it can transport the maximum amount of oxygen from the lungs to the rest of the body. A muscle cells contains many more mitochondrial organelles than normal cells and are able to contract producing movement. How is a sperm specialised to perform its function ...List three things ? Specialised cells in animals: Science Interactive LTD Copyright 2005 Word bank: thin electrical nucleus Sperm cells can propel themselves locating the female egg cell prior to fertilisation as well as carrying paternal DNA. They also have a streamlined head. Sperm cell Muscle cells contract providing movement. They are also rich in mitochondria. This allows them to respire glucose with oxygen producing energy. Nerve cells form connections with other nerve cells, carry impulses along a huge neural network that connect and coordinate our actions and thoughts. Red blood cells contain haemoglobin, have a biconcave shape and no nucleus. They carry oxygen from the lung surface to the rest of the body Notes Diagram Cell Red blood cell Nerve cell Muscle cells

Specialised cells in plants As in animals, plant cells are also designed for the function they play as part of the millions of cells that work together to support life and produce food in green plants. A root hair cell , for example is long and extremely thin to aid the uptake of w_______ and dissolved minerals like nitrates and phosphates from the s______. The leaf palisade cell contains many chloroplast organelles which during photosynthesis produces glucose and o________ from carbon dioxide and water. Which other cells have large surface areas to aid absorption ? Specialised cells in plants: Science Interactive LTD Copyright 2005 Word bank: water sun oxygen Pollen cells, the male gametes in plants are normally transferred to the female carpel by insects. Pollen carries the genetic information to create a new plant. Pollen cell Stomata cells found on the underside of green leaves allows the exchange of water, carbon dioxide and oxygen through the leaf during photosynthesis. Water moves up the stem through the xylem vessels. They are long tubes reaching from the roots to the leaf tissue. Water moves in xylem cells by capillary action. Green leaves contain many palisade cells which are rich in chloroplasts that enable photosynthesis to occur. Why do root cells not have these cell parts ? Notes Diagram Cell Palisade cells Xylem cells Stomata cell

Cell size in plants and animals Cells in plants and animals vary in size. To visualize plant or animal cells we need to use a m___________. Animal cells on average, tend to be smaller and less regular in shape, when compared to plant cells. Both plant and animal cells grow and divide before becoming too large. Cells that are too large will have a reduced surface area to volume ratio . A small surface area to volume ratio reduces the amount of o__________ and nutrients that can be absorbed across its surface membrane. Cells must then divide or die. This is called mitosis . Cell size and mitosis: Science Interactive LTD Copyright 2005 Word bank: microscope oxygen Mitosis Parent cell 2 Daughter cells DNA replicates Chromosomes separate Stage one Stage four Stage two Stage three 2n 2n 4n 2n As the cell volume increases, the ratio of surface area to volume ratio deceases reducing the cells ability to allow sufficient nutrients and oxygen across the cell membrane. Cells are able to divide and clone themselves during mitosis. Over a billion cells an hour are replaced in your body by cells dividing. Cell division in plants and animals Photograph of plant palisade cells. They are magnified 100 times . Find their size using the same method. Are they smaller or larger than human cheek cells ? Photograph of human cheek cells. They are magnified 250 times . Use a ruler to measure their length. Now divide by 250 to find their real size. Notes Diagram Cell Typical animal cells Typical plant cells

Mitosis for replacing cells New cells are needed for you to grow and repair. These are made by cell divisions called mitosis. During mitosis, a cell d_________ and forms two identical clone cells. The human body produces up to one billion cells like this every hour replacing old worn out cells. New s______, muscle, blood, and nerve cells are all produced this way. Some species reproduce using mitosis. Bacteria, for example multiply using mitosis. What are the advantages of reproducing asexually ? Replacing cells by mitosis: Science Interactive LTD Copyright 2005 Word bank: division skin Embryo grow by cloning cells. A single zygote leads to the formation of an embryo’s many millions of cells during pregnancy. Embryo growth Skins cells are lost and replaced due to normal wear and tear by mitosis. Every day we lose about 100 million skin cells. New skin cells Bacteria reproduce multiply and spread by cloning them-selves. Each cell is identical to the original bacterial cell. Bacteria Notes Diagram A human contains many billions of cells. Each hour of every day, we replace over one billion cells in our body. Human Blood cells last only about 90 days before they need to be replaced by the marrow of the long bones. Blood cells

Mitosis Normal cell division Mitosis occurs during growth and repair. Mitosis leads to formation of new identical cells. Producing c______ or identical cells has several advantages. They behave just like the old ones and they don’t require anything but the original cell. What other advantages are there to producing identical clone cells ? Stages in mitosis: Science Interactive LTD Copyright 2005 Word bank: clone Mitosis Parent cell 2 Daughter cells DNA replicates Chromosomes separate Stage one Stage four Stage two Stage three 2n 2n 4n 2n Mitosis in plants Notes Diagram Stage one: Chromosomes become visible and double inside the nucleus. The cell now contains 46 pairs of chromosomes. Stage two: The chromosomes move to the centre and line up before separation. Stage three: Each set of chromosomes separates moving to the cell poles before cell division. Stage four: The cell divides, producing two clone cells each containing 23 pairs of chromosomes. In the shoots and tips of plants new cells are formed during mitotic cell divisions. Each daughter cell is identical to the original cell. This picture shows several cells in various stages of mitosis. Mitosis (normal cell division)

Meiosis gametes in humans Meiosis leads to the formation of only two types of cells. Meiosis in males forms the s______ and in females the o______ or egg cells. Meiosis halves the number of chromosomes, so that when the sperm and egg fuse, the fertilised zygote will have the correct number of chromosomes (23 chromosomal pairs). Meiosis also produces random gene mixing leading to variation of human traits in new individuals. Gamete production in the male and female: sperm egg Science Interactive LTD Copyright 2005 Word bank: sperm ovum All of these 31,000 genes code for all the traits and characteristics that make human life unique. Cells now divide by mitosis. After fertilisation, all cells of the developing embryo now contain 23 pairs of chromosomes with over 31,000 genes. Sperm and egg cells are haploid with only 23 single chromosomes only half the normal number Gametes cells (sperm and egg) are produced by the testis and ovaries in the male and female. Pregnancy Embryo Fertilisation Gametes

Meiosis Reductive cell division During meiosis, the number of chromosomes are halved so that the s______ and egg carries 23 single chromosomes. During meiosis, paternal genes that code for your characteristics randomly mix, so that we are all not the same. Name the cells in plants that are produces by the process of meiosis ? Stages in meiosis: Science Interactive LTD Copyright 2005 Word bank: sperm Sperm production Notes Diagram Stage 1: Chromosomes double and randomly mix inside the nucleus. The cell now contains 46 pairs of chromosomes. Stage 2: The chromosomes move to the centre and line up before separation. Stage 3: The cell divides, producing two new cells each containing 23 pairs of chromosomes. Stage 4: The two daughter cells divide again halving the number of chromosomes. Each gamete now contains only 23 single chromosomes. A sperm cell carries 23 single chromosomes and fuses with an egg cell which also carries 23 single chromosomes to form a zygote, which now carries the normal diploid number of chromosomes. Meiosis (reductive cell division) Meiosis Stage one Stage four Stage two Stage three 2n n 4n 2n Parent cell & replicates 2 daughter cells 4 daughter cells DNA mixes

Meiosis Determining sex by chromosomes Your chromosomes also determine what sex you are at b_______. In humans there are 23 pairs of chromosomes found in every cell. 22 pairs are identical, but pair 23 do not match. Pair 23 are called the sex chromosomes. All eggs from the female contain the X chromosome, sperm from the male contain either the X or Y chromosome. At f_____________, the egg may join with either an X or Y sperm producing equal numbers of males ( XY ) or females ( XX ). What are the gametes cells called in plants ? Inheritance of the sex chromosomes: Science Interactive LTD Copyright 2005 Word bank: birth fertilisation During fertilisation, the number of chromosomes are restored to their normal diploid number (23 pairs) The embryo now grows by normal cell division called mitosis. The gamete cells (sperm and egg) carry only 23 single chromosomes. They are haploid cells. Your sex is determined at the moment of fertilisation by the male sperm. An X carrying sperm produces a girl, and a Y carrying sperm produces a boy. There is a 50: 50 chance of either sex. Sex inheritance Gamete cells Female Male

Meiosis gametes in plants Pollination is the transfer of pollen, the male sex cells from the a_________ of the stamen by b____ or insects to the surface of the female c_________. Once the pollen sex cells have landed on the female carpel, pollination has been achieved. Flowering plants contain both female and male reproductive organs and can either self or cross pollinate. Following fertilisation, where the ovule and pollen cell fuse, the seed begins to develop surrounded by the swollen ovule which forms the f_______. It is the function of the fruit to disperse the seed. What is this organ’s role in the plant life cycle ? Plant reproductive system: Science Interactive LTD Copyright 2005 Word bank: anther bees carpel fruit The stamen is the plant male reproductive organ which contains many millions of microscopic pollen cells. Male anther Flowering plants have both male and female reproductive organs. Plants can self or cross pollinate. The egg cells or ovules contain the maternal genes and are held in the ovule, part of the female carpel. Pollen, the male sex cells contain the paternal genes and are held on the anther which is part of the male stamen. Notes Diagram Pollen cells Female carpel Reproductive system

Meiosis Variation in humans one Humans have many of their genes which are common to us all. Over 99% of our genes in all the races are shared. Only 1% of human g_______ are unique and different. These genes code for differences in the colour of skin, eyes, hair and other features like the shape of our faces. Unless you’re an identical twin, your genes, your traits and you are unique amongst the other 5.5 billion human beings found on this planet. What are the advantages of variation in a species like humans ? Variation in humans: Science Interactive LTD Copyright 2005 Word bank: genes Variation in humans (traits such as skin and eye colour) occur due to the random mixing of DNA during meiosis ensuring that no egg or sperm carry exactly the same genes or DNA and of course during fertilisation, when the genes from your mother and father mix to form you. Notes Japanese Maori Arab Diagram Masai warrior Aborigine

Meiosis Variation in humans two Variation in the human race is caused by differences in your genes, caused by the random m______ of DNA during the production of sperm and egg and of course when the genes from your father and mother join during fertilisation. Your mother and father both share exactly 50% of your DNA and are your closest biological relatives. Brothers and sisters can share up to 50% of their DNA, but the figure is usually only around 25%. Why do brothers and sisters look very similar to one another ? Variation in humans: Science Interactive LTD Copyright 2005 Word bank: mixing Look around you in class, we all have certain similarities, but we are all unique. We belong to the same species, can reproduce with one another but are all different. Some people are taller or heavier or have different colour hair, skin or eyes. This is called variation. This is because we all have different genes in our cells from our parents. Notes South American Europe (south) Asian Diagram African Europe (North)

1: Define the following terms: Chromosome, Gene, Allele, Characteristic, Diploid, Haploid, Trait, Genotype, Phenotype, Mutation, Recessive and Dominant. 2: Look at the three pictures below. Complete the table: 3: Answer the following: a) Give 3 examples of human traits or characteristics b) Give 3 examples of traits or characteristics in plants. c) Name two cells that have a diploid number of chromosomes and two cells that have a haploid number of chromosomes. Do any cells in humans have no chromosomes. d) From the following, decide whether each cell is the result of mitotic or meiotic cell division. Extension questions and homework Science Interactive LTD Copyright 2005 Description Production of sperm and egg Plant cells dividing at shoot tip Embryo growing during pregnancy Mitosis/Meiosis Picture Bacteria Sperm Muscle cell Pollen Plant ovum Sperm cell Skin cell Blood cell

4: The diagram below shows how the sex of a child is determined by the chromosomes inherited from both parents. (a) All human cells contain 46 chromosomes. How many chromosomes are there in human egg or sperm cells. (b) Explain why either a daughter or a son will share some of the characteristics from both parents. (c) Explain why your parents are your closest living relatives. (d) What type of cell division leads to the formation of an embryo from a zygote during pregnancy. 5: Chromosomes occur in pairs in all cells except gametes. (a) What are alleles (b) Why are there two alleles for each characteristic. (c) Explain what is meant by dominant and recessive alleles. (d) The characteristics of humans are either inherited, or are caused by environmental influences. [Blood group, Weight, Eye-colour, Gender and Accidental loss of arm] (i) Which features are controlled by environmental influences (ii) Name one that is controlled by inheritance only (iii) One that is controlled by both. 6: A plant can either self or cross pollinate. Answer the following questions: (a) Which process (self or cross) leads to the production of (i) Identical offspring (ii) Different offspring. (b) List the advantages and disadvantages of asexual and sexual reproduction in plants. Internet: Go to google.co.uk and find about how cloning in plants is used by commercial growers to improve the quality and yield of a particular crop. Are there any disadvantages to cloning plants for commercial reasons. Science Interactive LTD Copyright 2005