2.1.6 Cell Division Biology OCR A Level

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  • Created by: Davina1st
  • Created on: 02-05-21 14:13
What are the three stages of interphase?
G1-first growth phase, organelles replicate and cell increases in size. S1-synthesis, DNA replicated. G2-second growth phase.
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What is interphase?
Long periods of growth and normal working separate divisions. Cells are not actively dividing , but producing enzymes and hormones whilst preparing for cell division.
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What processes occur during interphase?
DNA is replicated and checked for errors, protein synthesis occurs in the cytoplasm, mitochondria grow and divide increasing number in cytoplasm, chloroplasts grow and divide in plant cells, normal metabolic processes occur.
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What is G₀?
The phase where the cell leaves the cycle, either permanently or temporarily. differentiation -cell is specialised and can no longer divide. The DNA may be damaged=permanent cell arrest. Age-number of cells in body increases=cancer.
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Why do checkpoints occur at various stages of the cell cycle?
To monitor and verify whether the processes at each phase of the cell cycle have been accurately completed before the cell is allowed to progress to the next stage.
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What are the three checkpoints of the cell cycle?
G1, G2 and pindle assembly checkpoint.
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When does the G1 checkpoint occur and what is checked?
The checkpoints is at the end of the G1 phase, before entry into the S phase. If it satisfies the requirements, it begins DNA replication. Cell size, nutrients, growth factors and DNA damage.
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When does the G2 checkpoint occur and what is checked?
At the end of G2 phase, before start of mitotic phase. Whether the DNA has been replicated without error. If passed, mitosis begins. Cell size, DNA replication and DNA damage.
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When does the spindle assembly checkpoint occur and what is checked?
Occurs at the point of mitosis where all chromosomes should be attached to spindles and have aligned (metaphase). Mitosis cannot go ahead until this point is passed. Check that chromosomes are attached to the spindles.
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What is the importance of mitosis?
Produces two identical daughter cells, for growth, replacement of damaged cells, repair of tissues in multicellular organisms. Each new cell has an exact copy of the DNA present in the parent cell. Necessary for asexual reproduction.
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What are chromatids?
Two identical copies of DNA (a chromosome) held together at a centromere.
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What is chromatin?
Uncondensed DNA in a complex of histones.
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What are chromosomes?
Structures of condensed and coiled DNA in the form of chromatin. Chromosomes become visible under the light microscope when cells are preparing to divide.
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The four stages of mitosis can be viewed under a light microscope? True or false?
True.
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What are the four stages of mitosis?
Prophase, metaphase, anaphase and telophase.
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What occurs during prophase? mitosis
Chromatin fibres begin to coil and condense to form chromosomes that stain and become visible. Nuclear membrane breaks down. Protein microtubules form spindles link poles of cell. Spindle fibres attach to centromeres and move chromosome to centre.
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What occurs during metaphase? mitosis
Chromosomes are moved by the spindle fibres to forma plane in the centre of the cell called the metaphase plate and then held in position.
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What occurs during anaphase? mitosis
Centromeres holding the pairs of chromatids in each chromosome divide. Chromatids are pulled apart to opposite poles of the cell by shortening spindle fibres. Creates v shapes chromatids.
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What occurs during telophase? mitosis
Chromatids have now reached opposite poles of the cell and are now called chromosomes. Nuclear envelope begins to form around them, chromosomes uncoil and nucleolus is formed. Cytokinesis can now begin.
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Describe cytokinesis in animal cells
A cleavage furrow forms around the middle of the cell. The cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse in the middle. forming two cells.
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Describe cytokinesis in plant cells
Plant cells have cell walls so it is not possibel for a cleavage furrow to form. Vesicles from golgi assemble at metaphase plate. Vesicles fuse with each other dividing the cell into two. New sections of cell wall form around the new cell.
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Give an example of two cells that reproduces by meiosis
Egg and sperm
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Give an example of a cell that divides by mitosis
Mitochondria
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What does haploid and diploid mean?
Normal cells have two chromosomes of each type (diploid). Gametes divide by meiosis so that each gamete contains half of the chromosome number of the parent cell (haploid)
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What is an allele?
Different versions of the same gene e.g. two genes which code for eye colour but one is blue and the other is brown.
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What is a homologous chromosome?
Matching sets of chromosomes, each chromosomes in a homologous pair has the same genes at the same loci.
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How are chromosomes separated during meiosis 1?
Reduction division when the pairs of homologous chromosomes are separated into two cells. Each intermediate cell will only contain one full set of genes instead of two so the cells are haploid.
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How are chromosomes separated during meiosis 2?
Similar to mitosis, pairs of chromatids in each daughter cell are separated forming two more cells. Four haploid cells produced in total.
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Chromosomes in meiosis
pair of homologous chromosomes, separated into two different cells, chromatids separated by further division into 4 cells each with a single chromatid.
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How does crossing over occur in meiosis?
Chromatids of homologous chromosomes twist around one another crossing over. Chiasmata - point of breakage. Equal portions of chromatid are exchanged.
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How does meiosis produce genetic variation?
Parent cell with homologous chromosomes experience crossing over, the homologous chromosomes are separated into different cells. Chromatids are separated further with all 4 cells having different genetic composition.
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How are multicellular organisms organised?
Specialised cells-tissues-organs-organ systems-whole organism.
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What is a differentiated cell?
They are specialised to carry out very specific functions.
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Give 3 examples of specialised animal cells
Erythrocytes, neutrophils and sperm cells.
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How are erythrocytes specialised to carry out their function?
Flattened biconcave shape which increases SA:V essential to role of transporting O2. No nuclei or other organelles which increases space available for haemoglobin. Flexible - squeeze through narrow capillaries.
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How are neutrophils specialised to carry out their function?
Essential role in immune system, multi-lobed nucleus which makes it easy to squeeze through gaps to get to the site of infection. Granular cytoplasm- contains lysosomes that contain enzymes used to attack pathogens.
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How are sperm cells specialised to carry out their function?
Male gametes, function to deliver genetic information to the female gamete. Have a flagellum so they are capable of movement and contain mitochondria for the energy to swim. Acrosome contains digestive enzymes-digest protective layers of ovum.
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Give an example of three specialised plant cells
Palisade cells, root hair cells and guard cells
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How is a palisade cell specialised to carry out its function?
Contain chloroplasts to absorb large amounts of light for photosynthesis. Rectangular box shapes to pack into a continuous layer, thin cell walls increasing rate of diffusion. Vacuole to maintain turgor pressure.
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How are root hair cells specialised to carry out their function?
Tips of roots and shoots, long extensions called root hairs. Increase SA of cell and maximises water uptake.
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How are guard cells specialised to carry out their function?
Pairs of guard cells on surfaces of leaves form small openings called stomata. Necessary for gas exchange, when guard cells lose water and become less swollen, they change shape and close stoma = less water loss. One side thicker not symmetrical
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What is a tissue?
A tissue is made up of a collection of differentiated cells that have specialised functions. As a result they are adapted for a particular function.
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What are the four main categories of tissues in animals?
Nervous tissue - adapted to support transmission of electrical impulses. Epithelial tissue- cover body surfaces, muscle-adapted to contract, connective tissue- adapted to hold other tissues together.
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What is an organ?
A collection of tissues that are adapted to perform a particular function.
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Organ systems are composed of one organ, true or false?
False - each organ system is composed of a number of organs working together to carry out a major function
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Give an example of some organ systems in animals?
Digestive system, cardiovascular system, gaseous exchange system.
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What is a stem cell?
An undifferentiated cell, that has the ability to become specialised.
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A stem cells ability to differentiate into different cell types is called...
Potency
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What does totipotent mean?
Stem cells that can differentiate into any type of cell. Can eventually produce a whole organism
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These stem cells can form all tissue types but not whole organisms, present in embryos. What kind of potency?
Pluripotent
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What does multipotent mean?
Stem cells that can only form a range of cells within a certain type of tissue.
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Embryos are a source of animal stem cells? true or false?
True embryonic stem cells are present at early stage of embryo development and are totipotent.
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Where are adult stem cells found and what kind of potency do they have?
Presnt throughout life from birht, multipotent.
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What is a source of plant stem cells?
Where growth is occurring, tips of roots and shoots.Can differentiate into different cells present in xylem and phloem tissue.
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Give 4 uses of stem cells
Can be transplanted to specific areas to treat diseases such as: heart disease, Parkinson's, birth defects and spinal injuries.
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How are squamous epithelium cells specialised to carry out their function?
Made up of squamous epithelial cells, very thin, only one cell thick which means rapid diffusion. Forms lining of the lungs for efficient exchange.
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How are ciliated epithelium cells specialised to carry out their function?
Have hair like structures, cilia, that move in a rhythm, lines the trachea can move mucus away from lungs.
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How is cartilage specialised to carry out its function?
Connective tissue found in outer ear, nose and between bones. Contains fibres of elastin and collage. Cartilage is firm and flexible prevents the ends of bones rubbing together.
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How is muscle specialised to carry out its function?
Muscle needs to be able to contract in order to move bones, which in turn move different parts of the body. Skeletal muscle fibres contain myofibrils which contain contractile proteins.
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What are the different types of tissues in plants?
Epidermis tissue adapted to cover plant surfaces and vascular tissue adapted for transport of water and nutrients.
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How is the epidermis specialised to carry out its function?
Single layer of closely packed cells covered in waterproof waxy cuticle to reduce loss of water. Stomata are present in epidermis which allow for gaseous exchange.
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How is xylem tissue specialised to carry out its function?
A type of vascular tissue responsible for transport of water and minerals throughout plants. Composed of vessel element elongate dead cells. Walls strengthened by lignin which provides structure.
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How is phloem tissue specialised to carry out its function?
A vascular tissue responsible the transport of organic nutrients from leaves and stems to where it is needed. Sieve tube cells and sieve tube plates.
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Card 2

Front

What is interphase?

Back

Long periods of growth and normal working separate divisions. Cells are not actively dividing , but producing enzymes and hormones whilst preparing for cell division.

Card 3

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What processes occur during interphase?

Back

Preview of the front of card 3

Card 4

Front

What is G₀?

Back

Preview of the front of card 4

Card 5

Front

Why do checkpoints occur at various stages of the cell cycle?

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