AS OCR biology - cell division, diversity and organisation
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| What is a nucleosome? | A package of chromatin made up of double-stranded DNA wrapped around a histone core
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| What is a histone? | A histone protein makes DNA compact so it fits in the nucleus - not present in prokaryotic cells
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| What is the cell cycle? | The events that take place when a parent cell divides to produce to new daughter cells that grow to full size and are genetically identical to each other and the parent cell. The new cells can be separate organisms or new cells in a multicellular organism
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| What are the main stages of the cell cycle? | Interphase, mitosis, cytokinesis, growth phase
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| What is interphase? | DNA replication and growth. G1- biosynthesis organelles replicated, proteins made, checkpoint. S - synthesis, chromosomes replicated so each consists of a pair of sister chromatids. G2- growth of developing cell, checkpoint to ensure cell is ready
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| What are sister chromatids? | Two replica strands of DNA - a chromosome is replicated to form two sister chromatids in interphase.
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| What is mitosis? | The process where two genetically identical daughter nuclei are produced from a parent cell nucleus.
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| What is the first stage of the cell cycle? | Prophase - sister chromatids supercoil (coil, thicken to 500nm, shorten) so can be seen under LM, take up stains, can be moved around in a cell. Nucleolus breaks down. Centriole divides- daughter centrioles move to opposite poles of the cell, form spindle
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| What is the spindle? | Protein fibres produced by centrioles in mitosis
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| Describe the second stage of mitosis. | Metaphase- sister chromatids line up at equator of spindle, become attached to a spindle thread by the centromere, and nuclear envelope breaks down.
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| Describe the third stage of mitosis. | Anaphase- centromere divides so chromatids split, spindle fibres contract and shorten pulling chromatids towards opposite poles of cell in v shape, each half of the cell receives one chromatid from each chromosome.
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| Describe the final stage of mitosis | Telophase- chromosomes reach poles of cell, nuclear envelope forms around each set of chromosomes, nucleoli form, spindle breaks down, chromosomes uncoil so can't be seen under lihgt microscope.
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| What is cytokinesis? | The cytoplasm splits producing two daughter cells with identical chromosomes.
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| How does mitosis/ cytokinesis occur in animals? | Occurs in all cells. Centrioles are present. Cytokinesis is out to in - microfibrils attach to cell surface and divide cell.
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| How does cytokinesis occur in plants? | Only in meristem cells. Centrioles are absent - tubulin protein threads are made in cytoplasm instead. Cytokinesis starts in to out - formation of cell plate (cell wall and cell membrane material) where spindle equator was, forms two separate cells.
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| What is the final stage of the cell cycle? | Growth stage - each cell grows to full size
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| What affects the speed of the cell cycle? | Species, cell type, availability of nutrients
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| How are mutations spotted? | Proof-reading enzymes check for mutations when chromosomes are being replicated.
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| What are the uses of mitosis? | Cloning, asexual reproduction (bacteria divide in half, some plants grow plantlets which grow into individual orgnaisms), growth in multicellular organisms, repair and replacement of damaged cells - new cells must be able to perform same function as old
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| What is cell differentiation? | Where cells in a multicellular organism become specialised to carry out a particular function
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| What is a tissue? | A group of specialised cells carrying out a particular function
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| What is an organ? | Several different types of specialised tissues working together to carry out a particular function
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| What is an organ system? | Several different organs working together to carry out a particular function
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| What is the function of xylem tissue? | Carries water and minerals around the plant for photosynthesis and supports the plant
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| What is the structure of xylem tissue? | Xylem vessels and parenchyma cells and fibres. Meristem cells eg. cambium differentiate into small cells that elongate, waterproofed + reinforced by lignin deposits that kill cell contents, ends of cells break down forming long tubes, wide lumen.
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| What is the function of phloem tissue? | Translocation - the movement of products of photosynthesis around the plant
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| What is the structure of phloem tissue? | Sieve tubes + companion cells. Meristem cells eg cambium differentiate into cells that elongate and line up to form a tube. Sieve plates between cells, allowing movement. Companion cells are metabolically active, next to sieve tube.
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| What is epithelia? | Animal tissues lining external surfaces and internal surfaces (endothelium)
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| What is the difference between simple and compound epithelia? | Simple epithelia are one cell thick, compound epithelia are several layers thick
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| How are epithelia kept together? | Layers of cells are held together by a non-cellular basement membrane made of collagen and glycoproteins which attaches epithelial cells to connective tissue
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| What are squamous epithelia? | Flat cells in alveoli and villi, provide quick and short diffusion pathway
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| What are ciliated epithelia? | Lined with cilia which waft mucus containing trapped organisms up trachea and eggs along oviduct
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| What is the general function of epithelia cells? | Resist physical damage, prevent entry of pathogens
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| What are the components and functions of a palisade cell in a leaf? | Upper epidermis- transparent so allows light to penetrate. Palisade mesophyll - contains lots of chloroplasts containing chlorophyll. Spongy mesophyll - large air spaces to allow circulation of gases. Lower epidermis- contains stomata for gas exchange
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| Continued | Guard cell- 1 on either side of each stoma, cell wall contains spiral thickenings of cellulose so when the cell is turgid the stoma opens, when the cell is flaccid stoma closes. Leaf vein system- xylem + phloem support leaf + carry substances around plant
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| How do organ systems work together in locomotion? | Muscular and skeletal systems work together to allow movement. Nervous system coordinates muscle movement. Nutrients and oxygen are taken from the circulatory system to provide energy, and these are received from the digestive and ventilation systems
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| What are the adaptations of spermatozoa? | Lots of mitochondria to produce ATP to provide energy for the movement of the undulipodium, haploid nucleus, streamlined shape, acrosome releases enzymes for the penetration of the egg
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| What is an emrbyonic stem cell? | An undifferentiated cell from an early stage of division of an embryo - it can differentiate to become any type of specialised cell (totipotent) and can divide by mitosis
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| What is an adult stem cell? | An undifferentiated cell found in bone marrow, can differentiate for form a few types of specialised cell (pluripotent) and can divide by mitosis. Can form erythrocytes and neutrophils
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| What are the structures of erythrocytes and neutrophils? | Erythrocytes - lack a nucleus and most organelles to make space for haemoglobin, biconcave disc shape increases surface area so oxygen diffuses in and out quickly. Neutrophils - lobed nucleus, lots of lysosomes containing lysozymes to digest pathogens
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| What are the adaptations of root hair cells? | Large surface area to maximise absorption of minerals and water, lots of protein pumps for facilitated diffusion and active transport, lots of mitochondria to provide ATP for active transport
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| What is meiosis? | The process of nuclear division where a diploid cell divides to produce 4 haploid daughter cells, which are all genetically different from each other and the parent cell and contain half teh number of chromosomes.
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| What are the stages of meiosis? | 2 nuclear divisions - one separates homologous chromosomes, the second separates sister chromatids. Crossing over of genetic material at the chiasmata causes genetic variation. Occurs in gonads and produces gametes
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| What is meant by the term 'pair of homologous chromosomes'? | Chromosomes with genes in the same loci, the alleles may differ
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| What are the main differences between meiosis and mitosis? | Mitosis produces 2 diploid cells, meiosis produces 4 haploid. Mitosis produces genetically identical cells with no variation, meiosis produces different cells with genetic variation. Mitosis has 1 nuclear division, meisosis has 2.
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| How do yeast reproduce? | Budding. Chromosomes replicate and separate inside the nuclear envelope. Organelles replicate and migrate into the bud with the nucleus. The small bud containing its share of chromosomes and organelles splits from the parent cell forming a bud scar
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