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Transcript
London Science Tuition 2.6 CELL DIVISION, CELL DIVERSITY AND CELL DIFFERENTIATION 2.6.1: Cell cycle and regulation By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: The cell cycle How the cell cycle is regulated The eukaryotic cell cycle Cells reproduce by duplicating their contents Two daughter cells are produced Can be observed under a microscope Cytokinesis refers to the splitting of the cytoplasm Nuclear and cytoplasmic division = M phase M phase takes up a short section of cell cycle Interphase takes up the majority of the cell cycle It contains check points and is where DNA is duplicated Figure 1: The cell cycle G1 and G2 act as check points Purpose is to prevent uncontrolled cell division that would lead to tumours Prevent cellular damage and repair DNA DNA is only duplicated once in each cycle and cannot be reversed Phase of cell cycle and checkpoints Events within the cell Questions: 1. List the purpose of checkpoints to control the cell cycle? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 2. Epithelial cells lining the intestine divide two or three times a day. Liver cells divide about once a year. In which parts of their cell cycle will liver cells differ from intestine epithelial cells? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 2.6.2: Mitosis By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: The main stages of mitosis Sections of plant tissue showing the cell cycle and stages of mitosis The significance of mitosis in life cycles The significance of mitosis in the life cycle Asexual reproduction Occurs in single celled protoctists and single celled fungi Aphids sometimes produce eggs by mitosis Allows growth in multicellular organisms All cells are genetically identical Allows tissue repair to muscle fibres and walls of blood vessels Main stages of mitosis Cytokinesis Once mitosis is complete, the cell splits into two so that each new cell contains a nucleus Plasma membrane folds inwards and nips into the cytoplasm in animal cells In plant cells, an end plate forms where the equator of the spindle was, and new plasma membrane and cell-wall form Once plant cells become specialised, they cannot divide Common mistakes made by students Students write that DNA is duplicated during mitosis. Incorrect, DNA is divided during mitosis Students write that chromosomes move to poles during anaphase 2. Incorrect, chromatids move to poles during anaphase Questions 1. Explain why plant palisade mesophyll cells cannot undergo mitosis? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 2. State three reasons why mitosis is necessary in the cell cycle? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 3. Describe the difference between a chromatid and a chromosome? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 2.6.3: Meiosis By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: The significance of meiosis in life cycles The main stages of meiosis Key definitions Haploid: Having only one set of chromosomes, represented by the symbol ‘n’ Homologous chromosomes: Matching chromosomes, containing the same genes at the same places (loci). They may contain different alleles for some of the genes Meiosis: Type of nuclear division that results in the formation of cells containing half the number of chromosomes of the parent cell Homologous chromosomes Body cells there are 46 chromosomes 23 from the mother, 23 from father Matching pairs are homologous Genes come in alternative forms called alleles Stages of meiosis Contains 2 rounds of division, each contains 4 stages In the first round of meiotic division you have prophase 1, metaphase 1, anaphase 1 and telophase 1 In the second round of meiotic division you have prophase 2, metaphase 2, anaphase 2 and telophase 2 Round two takes place at a right angles plane compared to round one Cytokinesis occurs at the end of the second division. Stages of Meiosis How meiosis produces genetic variation/significance in life cycles Crossing over during prophase 1 shuffles alleles Independent assortment of chromosomes in anaphase 1 leads to random distribution of maternal and paternal chromosomes of each pair Independent assortment of chromatids in anaphase 2 leads to further random distribution of genetic material Haploid gametes are produced, which can undergo random fusion with gametes derived from another organism of the same species Questions 1. Explain why sexual reproduction involves meiosis? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 2. Why is genetic variation good for populations of living organisms? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 3. What are the products of meiosis? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 2.6.4: Diversity in animal cells By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: How cells of multicellular organisms are specialised for particular functions The features and differentiation of stem cells The production of erythrocytes and neutrophils derived from stem cells in bone marrow Key Definitions Differentiation: Process by which stem cells become specialised into different types of cell Epithelial cells: Cells that constitute linings of surfaces and cavities Stem cell: Unspecialised cell able to express all of its genes and divide by mitosis The need for cell differentiation and specialisation Small organisms need a large surface area: volume ratio Obtain nutrients and gases through simple diffusion Multicellular organisms are larger and therefore have a smaller SA/V ratio Need specialised cells to carry out functions Differentiation Multicellular organisms start off as zygotes Results when an ovum is fertilised by a spermatozoan After several divisions an embryo forms The embryonic cells differentiate as certain genes are switched off and other genes may be expressed more The proportions of the different organelles differs from those of other cells The shape of the cell and contents change Specialised animal cells Erythrocytes – very small, 7.5 micrometres in diameter, large SA:V, oxygen can diffuse across the membranes quickly They are flexible Neutrophils make up 50% of white blood cells in your body, they are twice the size of erythrocytes and contain multi-lobed nuclei They travel towards infected sites via chemotaxis Ingest bacteria via phagocytosis Spermatozoa Lots of mitochondria to carry out respiration Long and thin Can swim and move easily Enzymes are released from acrosome Epithelial cells are thin and flat Question 1. How are sperm adapted to their function? …………………………………………………………………………………………………………… ………………………………............................................................................. 2.6.5: Cell diversity in plants By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: How cells of multicellular organisms are specialised for particular functions Palisade cells Where photosynthesis occurs Long and cylindrical so they are tightly packed together Large vacuole to push chloroplasts nearer membrane Contain cytoskeleton to move chloroplasts Guard Cells Light energy is used to produce ATP ATP actively transports potassium ions from surrounding epidermal cells by osmosis Water enters guard cells via osmosis from neighbouring cells Guard cells swell causing stomata to open, enabling gaseous exchange Root hair cells Root hair cells are epidermal cells on the outer layer of young plant roots Hair like projections increase surface area for absorption of water Have specialised carrier proteins for active transport of ions into cell Lowers water potential and triggers water absorption via osmosis Xylem and phloem Xylem and phloem form the vascular tissue of plants Adapted for function e.g. xylem vessels are hollow Question: Suggest why plants die if their roots are in waterlogged soil for several days? ……………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………… 2.6.6: Animal tissues By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: The organisation of cells into tissues Key Definitions Tissue: A group of cells that work together to perform a specific function/set of functions The four main types of tissue Epithelial – This is the lining of tissue Connective Tissue – These hold structures together and provide support, e.g. blood, bone and cartilage Muscle Tissue – Made of cells that are specialised to contract and cause movement Nervous Tissue – Made of cells specialised to conduct electrical impulses Epithelial Tissue Makes up vessels and respiratory systems Adjacent cells are bound to each other Cells receive nutrients by diffusion from tissue fluid Some epithelial cells have smooth surfaces, some have projections Function in absorption, filtration and excretion Connective Tissue Widely distributed in the body It consists of a non-living extracellular matrix containing proteins Matrix separates living cells within the tissue and enables the withstanding of forces e.g. weight Immature cells in cartilage are called chondroblasts They can divide by mitosis and secrete the extracellular matrix Hyaline cartilage forms the embryonic skeleton, covers the ends of long bones in adults and found in nose/trachea Muscle Tissue Muscle tissue is well vascularised (has many blood vessels) Muscle cells are called fibres Contain myosin and actin Skeletal muscle is packaged by connective tissue Cardiac muscle makes up the walls of the heart to pump blood Question: 1. Cartilage tissue is not vascularised. Suggest how the cells in this tissue may receive nutrients? ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… 2.6.7: Plant tissues and organs By the end of this topic, all students should be able to demonstrate and apply understanding of: The organisation of cells into tissues, organs and organ systems The production of xylem vessels and phloem sieve tubes Key Definitions Meristem: Area of unspecialised cells within a plant that can be divide and differentiate into other cell types Organ: Collection of tissues working together to perform a function/related functions Xylem: Tissue that carries water and mineral ions from the roots to all parts of the plant Epidermal Tissue This is the equivalent to epithelial tissue in animals. It consists of flattened cells that apart from the guard cells, lack chloroplasts and form a protective covering over leaves, stems and roots. Some epidermal cells also have walls impregnated with a waxy cuticle Vascular Tissue Vascular tissue is concerned with transport There are two sorts – xylem and phloem, both present in vascular bundles Xylem vessels carry water and minerals from roots to all parts of the plant Phloem sieve tubes transfer the products of photosynthesis, in solution, from leaves to parts of the plant that do not photosynthesise, such as roots, flowers and growing shoots Meristemic Tissue Contains stem cells It is found at root and shoot tips These are called meristems Cells in meristems have thin walls containing very little cellulose Do not have chloroplasts Do not have a large vacuole Can divide by mitosis and differentiate into other types of cells The production of xylem vessels and sieve tubes New cells arise at meristem by mitosis Cambium differentiates into xylem and phloem Lignin reinforces walls of xylem and ensures it doesn’t break. It also allows a continuous stream of water to pass up the xylem Cambium differentiates into phloem by forming sieve tube elements or companion cells which maintain their organelles for metabolic activity Plant Organ Leaf Root Stem Flower Main Functions 2.6.8: Organs and organ systems in animals By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: The organisation of cells into tissues, organs and organ systems A number of organs working together make up an organ system The skin is the largest organ in the body System Digestive Circulatory Respiratory Urinary Integumentary Musculo-skeletal system Immune system Nervous System Endocrine System Reproductive System Lymph System Organs and tissues involved Examples of life processes carried out 2.6.9: Stem Cells and their potential uses By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: The features and differentiation of stem cells The potential uses of stem cells in research and medicine Key Definitions Stem Cell: Unspecialised cell able to express all of its genes and divide by mitosis Stem Cells Undifferentiated Can become any type of cell Are able to express all of their genes Can develop into specialised cells Sources of stem cells There are different types of stem cells Embryonic stem cells which are present in early development Stem cells in umbilical cord blood Pluripotent cells can also be produced Potential uses of stem cells Stem cells from bone marrow are extensively used in bone marrow transplants to treat diseases of the blood such as sickle cell anaemia Patients bone marrow cells can be extracted and reinserted after treatment Can be used in chemical testing as opposed to using animals Repair of damaged tissues or replacement of lost tissues Stem cells have been used to treat mice with type 1 diabetes Bone marrow stem cells can be sued to treat liver disease There is potential for treatment of Alzheimer and other diseases like arthritis in the near future. 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