Cell structure and division

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What are prokaryotic cells?
Single celled organisms without a nucleus or membrane bound organelles in their cytoplasm.
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What are eukaryotic cells?
Complex cells with membrane bound organelles such as a nucleus.
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What are eukaryotic organisms?
Multi cellular organisms made up of eukaryotic cells
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What organelles does a plant cell have that an animal cells doesn't?
1) cellulose cell wall with plasmodesmata (channels for exchanging substances between adjacent cells. 2) A vacuole. 3) Chloroplasts
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What are chloroplasts?
Organelles involves in photosynthesis. Small flattened structure in plant and algal cells.
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What is the structure of a chloroplast?
Flattened structure. Surrounded by a double membrane and also has membranes inside called thylakoid membranes. Thylakoids are stacked up in some parts of the chloroplast to form grana. Grana are linked together by lamellae.
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What are lamellae?
Thin, flat pieces of thylakoid membrane inside a chloroplast.
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What are the differences between plant cells and algal cells?
The chloroplasts in algal cells are different shapes and sizes. E.g some algal cells only have one large chloroplast rather than several little ones.
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What are the differences between plant cells and fungal cells?
Their cell walls are made of chitin. They don't have chloroplasts (don't photosynthesise)
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Describe the cell surface membrane.
Found on surface of animal cells and just inside the cell walls of other cells. Made mainly of lipids and proteins.
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What are the main functions of the cell surface membrane?
Regulates the movement of substances into and out of a cell. It has receptor molecules on it, which allow it to respond to chemicals like hormones.
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Describe a nucleus.
Large organelles surrounded by a nuclear envelope (double membrane), which contains many pores. The nucleus contains chromosomes and one or more structure/s called a nucleolus.
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What is the function of the nucleus?
Control's the cells activities (by controlling the transcription of DNA). Contains instructions to make proteins. Pores allow substances to move between the nucleus and cytoplasm. Nucleolus makes ribosomes.
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Describe a mitochondria.
Usually oval-shaped. Have a double membrane - inner one folded to form structures called cristae. Inside is the matrix, which contains enzymes involved in respiration.
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What is the function of mitochondrion?
The site of aerobic respiration. Aerobic respiration produces ATP- a common source of energy in the cell. Found in large numbers in very active cells that need a lot of energy.
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Describe the golgi apparatus.
A group of fluid- filled membrane-bound flattened sacs. Vesicles are often seen at the edges of the sacs.
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What are the functions of the golgi apparatus?
Processes and packages new lipids and proteins. Also makes lysosomes.
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Describe a golgi vesicle.
Small fluid-filled sac in the cytoplasm. It is membrane bound and made by the golgi apparatus.
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What is the function of a golgi vesicle?
Stores lipids and proteins made by the Golgi apparatus and transports them out of the cdell via the cell-surface membrane.
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Describe a lysosome.
A round organelle surrounded by a membrane. No clear internal structure. A type of golgi vesicle.
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What are the functions of lysosomes?
Contains digestive enzymes called lysosozymes. These are kept seperate from the cytoplasm by the surrounding membrane and can be used to digest invading cells or to break down components of the cell.
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Describe a ribosome.
Very small organelle that floats freely in the cytoplasm or is attached to the rough endoplasmic recticulum. Not membrane bound. Made up of proteins and RNA.
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What is the function of a ribosome?
Makes proteins.
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Describe the rough endoplasmic recticulum.
System of membrane enclosing a fluid filled space. Surface is covered with ribosomes.
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What is the function of the RER?
Folds and processes proteins made by the ribosomes.
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Describe the smooth endoplasmic recticulum.
System of membrane enclosing a fluid filled space. No ribosomes on its surface.
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Describe the cell wall.
Rigid structure that surrounds cells in plants, algae and fungi. In plants and algae its made mostly of the carbohydrate cellulose but is made of chitin in fungal cells.
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Describe the cell vacuole (plants).
Membrane-bound organelle found in the cytoplasm. Contains cells sap- a weak solution of sugar and salts. The surrounding membrane is called the tonoplast.
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What is the function of the cell vacuole?
Helps maintain pressure inside the cell and keeps the cell rigid- which stops plants wilting. Also involved in the isolation of unwanted chemicals inside the cell.
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How is the small intestine adapted to absorb food efficiently?
The walls have lots of villi(finger- like projections) that increase surface area for absorption. Epithelial cells on surface of villi have folds in membrane called micro-villi which increase surface area more. Lots of mitochondria.
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How are red blood cells adapted to carry oxygen around the body?
No nucleus to make mpore room for the oxygen carrying compound, haemoglobin.
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How are sperm cells adapted to suit their function?
Lots of mitochondria for energy to propel themselves towards an egg.
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What is tissue?
A group of specialised cells working together to perform a particular function.
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What are organs?
A group of tissues.
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What is the difference between the cytoplasm of a eukaryotic cell and the cytoplasm or a prokaryotic cell?
Prokaryotic cells have smaller ribosomes in the cytoplasm.
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What is the flagellum and what is its structure?
A long hair-like structure that rotates around to make prokaryotic cells move. Not all prokaryotic cells have a flagellum and some have more than one.
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What is the difference between eukaryotic and prokaryotic DNA?
Prokaryotic DNA floats freely in the cytoplasm. It's circular DNA, present as one long coiled up strand and is not attached to any histone proteins.
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What are plasmids?
Small loops of DNA in prokaryotic cells that contain genes for things like antibiotic resistance and can be passes between prokaryotes. Not always present and some have several.
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Describe a capsule and explain its use in a prokaryotic cell.
A capsule made up of secreted slime. It helps protect the bacteria from attacks by cells of the immune system.
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What is the cell wall of prokaryotic cells made of?
A polymer called murein. It is a glycoprotein- a protein with a carbohydrate attached.
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How big are prokaryotic cells?
Extremely small- less than 2 micro metres in diameter. About 50x smaller than some eukaryotic cells.
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Describe prokaryotic cell replication.
1) Circular DNA(once) +plasmids(several times) replicate. 2) Cell gets bigger and DNA loops move to opposite poles. 3) cytoplasm divides and new cell walls form. 4)Produces two identical daughter cells. One main DNA but variable plasmids.
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Describe the structure of a virus.
A cellular- not cells. Nucleic acid surrounded by protein. No cell surface membrane, no cytoplasm or ribosomes. Protein coat- capsid with attachment proteins sticking out from it. Smaller than bacteria.
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What is the function of attachment proteins?
Let the virus cling to a suitable host cell.
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How do viruses reproduce?
By invading other cells and using hijacking the cells own 'material' to replicate.
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Describe viral replication.
1. Virus attaches to host cell receptor proteins. 2. Genetic material released into host cell. 3. Genetic material and proteins replicated by host cell 'machinery'. 4. Virus components assemble. 5.Replicated virus released from host cell.
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Why can some viruses only infect one type of cell?
Different viruses have different attachment proteins which are complementary to different receptor proteins.
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What is the formula for calculating magnification?
Magnification= size of image/ size of real object
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How do you convert millimeters to micrometers to nanometres?
mm - x1000 - micrometres - x1000- nanometres
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What is resolution?
How detailed the image is. How well a microscope distinguishes between two points that are close together.
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What is magnification?
How much bigger the image is than the specimen.
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Describe an optical microscope.
Use light to form an image. Max resolution of 0.2 micrometres. Can't see organelles smaller than this.
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What organelles cannot be seen through an optical microscope?
Ribosomes, endoplasmic recticulum and lysosomes. Can see mitochondria but not in perfect detail.
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Describe an electron microscope.
Use electrons to form an image. Higher resolution than optical microscopes. Max resolution of about 0.0002 - 1000x higher than optical. Produce balck and white images - often coloured by a computer.
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What are the two types of electron microscope?
Transmission and Scanning
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How do transmission electron microscopes work?
Use eslectromagnets to focus a beam of electrons, which is then transmitted through the specimen. Denser parts of the specimen absorb more electrons so appear darker.
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What are the advantages and disadvantages of using a transmission electron microscope?
Adv = Produce high resolution images so you can see the internal structure of organelles like chloroplasts. Disadv= Got to view spcimen in a vacuum so no good for looking at living organisms. Can only be used on thin specimens.
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How do scanning electron microscopes work?
Scan a beam of electrons through the specimen. Knocks off elesctrons from the specimen which are gathered in a cathode ray tube to form an image. Images show the surface of the specimen and can be 3D.
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What are the advantages and disadvantages of using a scanning electron microscope?
Adv= can be used on thick specimens. Disadv= Lower resolution that TEMs. Only used on non living organisms.
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What is a temporary mount?
Where a specimen is suspended in a drop of liquid on the slide.
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Why do you need to use a thin specimen when preparing a microscope slide?
The specimen needs to let light through it to see it clearly under the microscope.
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What are stains used for when preparing a microscope slide?
Highlighting objects in a cell.
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What are microscope aretefacts?
Things you can see down a microscope that aren;t part of tge specimen you're looking at.
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How did the first scientists distinguish between artefacts and organeels?
Preparing the specimens in many different ways.
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What is cell fractionalisation?
Separating organelles from the rest of the cell.
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What are the three steps of cell fractionalisation?
Homogenisation- breaking up the cells. Filtration- removing big bits. Ultracentrifugation- separating the organelles.
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How is homogenisation done?
Vibrating the cells or grinding them up in a blender to release organelles into solution. Solution kept ice cold- reduce effects of enzymes that break down organelles. Isotonic solution- prevent damage to organelles by osmosis. Buffer- maintain pH
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How is filtration done?
Filtered through gauze to separate large cell debris or tissue debris from the organelles. Organelles are small so pass through the gauze.
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How is ultracentrifugation done?
Cell fragments in tube- put into centrifuge- low speed. Heaviset organelles flung to bottom. Form thick sediment- pellet. Rest suspended in fluid- supernatant. Supernatant drained and centrifuge at higher speed. Repeated until all separated.
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What are the orders of organelles from heaviest to lightest?
nuclei, mitochondria, lysosomes, endoplasmic recticulum, ribosomes. Plant cells mitochondria second heaviest.
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What are the two stages of the cell cycle?
Interphase and mitosis
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Describe the three stages of cell growth in interphase.
G1- Gap phase 1- cell grows + new organelles and proteins made. S- synthesis- cell replicates DNA. G2- gap phase 2- cell continues growing and proteins needed for cell division made.
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What are the four division stages of mitosis?
Prophase, metaphase, anaphase and telophase
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Describe the structure of chromosomes in mitosis.
Chromosomes made into two strands joined in middle by a centromere. Separate strands= chromatids. Two strands on same chromosome = sister chromatids.
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Why are there two strands on the same chromosome before a cell divides by mitosis?
Because each chromosome has already made an identical copy of itself during interphase.
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Describe what happens in prophase.
Chromosomes condense and get shorter and fatter. Tiny bundles of proteins- centrioles- move to opposite poles- from network of protein fibres across cell called spindles. Nuclear envelope breaks down and chromosome lie free in cytoplasm.
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Describe what happens in metaphase.
Chromosomes- each with 2 chromatids- line up along middle of cell and become attached tot he spindle by their centromere.
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Describe what happens in anaphase.
Centromeres divide, seperating each pair of sister chromatids. Spindles contract and chromosomes pulled to opposite poles by spindle, centomeres first. Makes chromatids look v shaped.
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Describe what happens in telophase.
Chromatids reach opposite ends of spindle. Uncoil and become long and thin again. NOw chromosomes again. Nuclear envel;ope forms around each group of chromosomes- now two nuclei. Cytoplasm divides and produces two new identical daughter cells.
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What is cancer?
A tumour that invades surrounding tissue. Cells grow out of control as it is a mutation in a gene that controls cell division.
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How do cancer treatments work?
Control rates of cell division by disrupting cell cycle. Kills the tumour cells, Can't distinguish between normal and cancer cells but likely to kill cancer cells as they divide more frequently.
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How do you calculate mitotic index?
number of cells with visible chromosomes/total number of cells observed.
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What is mitotic index?
The proportion of cells in a tissue sample that are undergoing mitosis.
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What are eukaryotic cells?


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