Cell Division

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What is interphase?	It is the longest phase in the cell cycle, where the cell is carrying out all its major functions and preparing for cell division.
What happens during interphase?	DNA is replicated and checked for errors, protein synthesis occurs in the cytoplasm, mitochondria grow and divide, chloroplasts grow and divide in plant and algal cell cytoplasm and the normal metabolic processes of the cell occur
Describe what happens during G1	This is the first stage of interphase, where the cell grows. Proteins are produced by organelles in the cytoplasm and organelles replicate. The cell increases in size.
Describe what happens during the synthesis phase	DNA is replicated in the nucleus
Describe what happens during G2	This the third stage of interphase. The cell continues to increase in size, energy stores are increased and the duplicated DNA is checked for errors
What is the mitotic phase?	It is the period of cell division
What is mitosis?	When the nucleus of a cell divides
What is cytokinesis?	When the cytoplasm divides and two cells are produced
What is G0?	When the cell leaves the cell cycle, either temporarily or permenantly
Describe reasons why a cell would go into G0	Differentiation - once a cell is differentiated it can no longer divide so it does not enter the cell cycle again. Damaged DNA - a damaged cell can no longer divide and enters a period of permanent cell arrest. Lymphocytes - in an immune response more lymphocytes are activated. Lymphocytes can enter G0 and be stimulated to go back into the cell cycle again when necessary
What is the role of checkpoints in the cell cycle?	They monitor and verify whether the processes at each phase of the cell cycle have been accurately completed before the cell can progress onto the next phase
What happens at the G1 checkpoint?	Just before the synthesis phase, the cell is checked for cell size, nutrients, growth factor and DNA damage. If the cell satisfies the requirements of this checkpoint it is triggered to begin replication
What happens at the G2 checkpoint?	At the end of the G2 phase, the DNA is checked for whether it has replicated without error. If this checkpoint is passed, the cell begins mitosis.
What occurs at the metaphase checkpoint?	The cell is checked that all the chromosomes are attached to spindles and have aligned during mitosis.
Where do chromatids join together?	At the centromere
What are the four stages of mitosis?	Prophase, metaphase, anaphase, telophase
What happens during prophase?	Chromatin fibres coil and condense to form chromosomes. The nucleolus disappears and the nuclear envelope breaks down. Protein microtubules form spindle shaped structures linking the poles of the cell. Two centrioles migrate to opposite poles of the cell, they help in the formation of the spindle. The spindle fibres attach to centromeres and move the chromosomes to the centre of the cell.
What happens during metaphase?	The chromosomes are moved by the spindle fibres to form a plane in the centre of the cell called the metaphase plate.
What happens during anaphase?	Centromeres holding the pairs of chromatids divide. The chromatids are separated and pulled to opposite sides of the cell.
What happens during telophase?	The chromatids reach the poles and are now called chromosomes. A nuclear envelope forms around the two bundles of chromosomes. Chromosomes start to uncoil and the nucleolus is formed. Cytokinesis begins.
What happens during cytokinesis in animal cells?	A cleavage furrow forms around the middle of the cell. The cell surface membrane is pulled inward by the cytoskeleton until it is close enough to fuse around the middle, forming two new cells.
What happens during cytokinesis in plant cells?	Vesicles from the Golgi apparatus assemble across the metaphase plate equator. The vesicles fuse with each other and the cell surface membrane. New sections of cell wall then form along the new sections of membrane.
What kind of cell is a gamete known as?	Haploid
What happens during meiosis 1?	This is the first division, where pairs of homologous chromosomes are separated into two cells. Each intermediate cell has one full set of genes instead of two, so the cells are haploid.
What happens during meiosis II?	This is the second division, where the pairs of chromatids present in each daughter cell are separated, forming two more cells. After meiosis II four haploid cells are produced.
What happens during prophase 1 in meiosis I?	Chromosomes condense, the nuclear envelope disintegrates, the nucleolus disappears and spindle formation begins. Homologous chromosomes pair up, forming bivalents. The movement of chromosomes through the cytoplasm as they are brought together causes chromatids to entangle. This is 'crossing over'.
What happens during metaphase 1?	The homologous pairs of chromosomes assemble along the metaphase plate (instead of individual chromosomes in mitosis). The orientation of the homologous pairs is random, the maternal or paternal chromosomes can end up facing either pole. This is independent assortment. This process causes lots of different combinations of alleles and results in genetic variation.
What happens during anaphase 1 during meiosis 1?	The homologous chromosomes are pulled to the opposite poles and chromatids stay joined together. Sections of DNA on sister chromatids that become entangled during crossing over break off and re-join, sometimes resulting in an exchange of DNA. The points at which the chromatids break off and re-join are called chiasmata. This causes more genetic variation as new combinations of alleles are created.
What happens during telophase 1 during meiosis I?	The chromosomes assemble at each pole and the nuclear envelope reforms. The chromosomes uncoil. The cell undergoes cytokinesis and forms two separate cells. The chromosome number is reduced from diploid to haploid.
What happens during prophase 2 in meiosis II?	The chromosomes, which still consist of two chromatids, condense and become visible. The nuclear envelope breaks down and spindle formation begins.
What happens during metaphase 2?	Individual chromosomes assemble on the metaphase plate. Chromatids are no longer identical because of crossing over, so the independent assortment again and more genetic variation.
what happens during anaphase 2?	This stage results in the chromatids of the individual chromosomes being pulled to opposite poles after division of the centromeres.
What happens during telophase 2?	Chromatids assemble at the poles and chromosomes uncoil to form chromatin. The nuclear envelope reforms and the nucleolus becomes visible. Cytokinesis occurs and four haploid cells are produced that are all genetically different to each other.
What are differentiated cells?	Cells that a specialised to carry out specific functions.
What is an erythrocyte? Describe its structure and function.	They are red blood cells. They have a flattened biconcave shape, which increases their surface area to volume ratio. This helps their role in transporting blood around the body. They do not have nuclei to increase the space available for haemoglobin. They are also flexible so they can squeeze through small capillaries.
What are neutrophils? Describe their structure and function.	They are a type of white blood cell which play an essential role in the immune system. They have a multi-lobed nucleus, which makes it easier to squeeze through small gaps to get to the site of infections. The granular cytoplasm contains many lysosomes that contain enzymes used to break down pathogens.
What is the function and structure of a sperm cell?	These are male gametes that deliver genetic information to the female gamete. The have a flagellum for movement and contain a lot of mitochondria to supply the energy needed to swim. The acrosome on the head of the sperm contains digestive enzymes, which are released to digest the protective layers around the ovum and allow the sperm to penetrate.
Describe the structure and function of palisade cells.	They are present in the mesophyll and contain chloroplasts to absorb large amounts of light for photosynthesis. They are a rectangular shape to allow them to be closely packed together. They have thin cell walls to increase the rate of diffusion of carbon dioxide. They have a large vacuole to maintain turgor pressure. Chloroplasts can move within the cytoplasm to absorb more light.
Describe the structure and function of root hair cells.	They are present along the surface of roots and have long extensions called root hairs. These increase the surface area of the cells. This allows the uptake of more water and minerals.
Describe the role and structure of guard cells.	There are pairs of these on the surfaces of leaves which form small openings called stomata. These allow carbon dioxide to enter the leaves. When guard cells lose water they become flaccid and change shape so the stoma closes to prevent water loss. They have a thick inner wall so the cells close when they go flaccid.
What is tissue?	A collection of differentiated cells that have a specialised function.
What are the four main categories of tissues in animals?	Nervous tissue, epithelial tissue, muscle tissue and connective tissue.
Describe the structure and function on squamous epithelium.	It is made up of specialised squamous epithelial cells. It is very thin to help with fast diffusion across a surface. It forms the lining of the lungs to allow rapid diffusion of oxygen into the blood.
Describe the structure and the role of ciliated epithelium.	It is made up of ciliated epithelial cells. They have hair like structures called cilia on one surface that beat rhythmically. They line the trachea and sweep mucous away from the lungs. Goblet cells are also present, which release mucous to trap any unwanted particles present in the air.
Describe the role and structure of cartilage.	It is a connective tissue found in the outer ear, nose and around joints. It contains fibres of elastin and collagen. It's firm and flexible. It's composed of chondrocyte cells embedded in an extra cellular matrix. It prevents bones from rubbing together and causing damage.
Describe the function and structure of muscle.	It is a tissue that can contract and relax in order to move bones. There are many different types of muscle fibres, such as skeletal muscle fibres (attached to bone) which contain myofibrils which contain contractile proteins.
What are the two main tissues in plants?	Epidermis tissue and vascular tissue
Describe the role and structure of epidermis?	It is a single layer of closely packed cells covering the surface of plants. It is covered by a waxy, waterproof cuticle to reduce water loss. Stomata are present in the epidermis.
What is the role and structure of xylem tissue?	It is a type of vascular tissue responsible for the transport of water and minerals. it is composed of vessel elements, which are elongated dead cells. The walls of the vessel are strengthened by lignin.
Describe the role and function of phloem tissue.	It is a type of vascular tissue in plants that is responsible for the transport of organic nutrients. It is composed of columns of sieve tube cells separated by perforated walls called sieve plates.
What is an organ?	A collection of tissues that are adapted to perform a particular function in an organism.
What is an organ system?	A number of organs working together to carry out a major function in the body.
What is potency?	A stem cells ability to differentiate into different cell types.
What are totipotent stem cells?	Stem cells that can differentiate into any type of cell.
What are pluripotent stem cells?	Stem cells that can form all tissue types but not whole organisms. They are present in early embryos and are the origin of the different types of tissue within an organism.
What are multipotent stem cells?	Stem cells that can only form a range of cells within a certain type of tissue.

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