Cells Flashcards
Describe the structure of the nucleus.
-A large organelle surrounded by a nuclear envelope (double membrane), which contains many pores.
-The nucleus contains chromosomes (made from protein-bound DNA)
-Nucleolus- small spherical region within the nucleoplasm that manufacture rRNA and assembles ribosomes.
Describe the function of the nucleus.
-Controls the cells activities (by controlling the transcription of DNA).
-Makes mRNA and tRNA.
-The pores allow substances to move between the nucleus and the cytoplasm.
-Nucleolus makes ribosomes.
Describe the structure of the cell-surface membrane.
Found on the surface of animal cells and just inside the cell wall of other cells.
Made mainly of lipids and protein.
Describe the function of the cell-surface membrane.
-Regulates the movement of substances into and out of the cell.
-Has receptor molecules on it, which allow it to respond to chemicals like hormones.
Describe the structure of the mitochondrion.
-Has a double membrane- the inner one is folded to form structures called cristae.
-Cristae increase the surface area for attachment of enzymes and other proteins involved in respiration.
-Inside is the matrix- contains lipids, proteins, ribosomes and DNA that allow the mitochondrion to control its production of proteins.
Describe the structure of chloroplasts.
-Small, flattened structure surrounded by a double membrane that is highly selective in what it allows to enter and leave- chloroplast envelope.
-The double membrane has membranes inside called thylakoid membranes that are stacked up in some parts to form grana. Grana are linked together by lamella- thin, flat pieces of thylakoid membrane.
-Stroma- fluid-filled matrix where the synthesis of sugars takes place. Also contains starch grains.
Describe the function of the mitochondrion.
-Site of aerobic respiration, producing ATP.
-Found in large numbers in cells that are very active and require a lot of energy (high level of metabolic activity).
Describe the function of chloroplasts.
-Granal membranes provide large surface area for attachment of chlorophyll- the site of photosynthesis.
-Fluid of stroma contains enzymes needed to make sugars.
Describe the structure of the Golgi apparatus.
-A group of fluid-filled membrane-bound flattened sacs. Vesicles are often seen at the edges of the sacs.
Describe the function of the Golgi apparatus.
-Processes and packages lipids and proteins (and adds carbohydrates to proteins to form glycoproteins.
-Makes lysosomes
-Produces secretory enzymes and carbohydrates.
Describe the structure of lysosomes.
A round organelle surrounded by a membrane, with no clear internal structure. It is formed when vesicles produced by the Golgi apparatus contain certain enzymes.
Describe the function of lysosomes.
-Contain hydrolytic enzymes. These are kept separate from the cytoplasm by the surrounding membrane, and can be used to:
-digest worn out organelles- useful chemicals they are made of can be re-used
-digest invading cells
Describe the structure and function of ribosomes.
-A small organelle that floats free in the cytoplasm or is attached to the rough ER. Made up of proteins and rRNA.
-80S- found in eukaryotic cells
-70S- found in prokaryotic cells, mitochondria and chloroplasts, slightly smaller.
-Has two subunits- one large and one small.
Site of protein synthesis.
Describe the structure and function of the Rough Endoplasmic Reticulum.
-A system of membranes enclosing a fluid-filled space.
-Has ribosomes on the surface.
-Provides a large SA for the synthesis of proteins.
-Provides a pathway for the transport of materials.
Folds and processes proteins that have been made at the ribosomes.
Describe the structure and function of the Smooth Endoplasmic Reticulum.
-Similar to RER, but with no ribosomes.
-Synthesises and processes lipids and carbohydrates.
Describe the structure of the cell wall.
-A rigid structure that surrounds cells in plants, algae and fungi.
Plants and algae- microfibrils from cellulose
Fungi- chitin
-A thin layer cements adjacent cells together.
Describe the function of the cell wall.
-Provides mechanical strength to prevent the cell from bursting under osmotic pressure and to the whole plant.
-Prevents cells from changing shape and supports them.
-Allow the movement of water.
Describe the structure of the vacuole (plants).
A membrane-bound organelle in the cytoplasm. It contains cell sap- a weak solution of mineral salts, sugars, amino acids, wastes and sometimes pigments.
The surrounding membrane is called the tonoplast.
Describe the function of the vacuole (plants).
-Helps to maintain pressure inside the cell and keep the cell rigid, stops plants wilting.
-Involved in the isolation of unwanted chemicals inside the cell.
-Sugars and amino acids can act as a temporary food store.
-Pigments may colour petals attracting pollinators.
Define magnification.
How much bigger a sample appears to be under the microscope than it is in real life.
What are the equations for magnification?
Total magnification= objective lens magnification x eyepiece lens magnification
Define resolution.
The ability to see two objects that are close together as separate objects.
The ability to see detail.
Compare and contrast light and electron microscopes.
LIGHT
Use light to form an image.
Have a maximum resolution of 0.2 micrometres.
Cannot see ribosomes, ER and lysosomes- sometimes can see mitochondria.
Maximum useful magnification x150.
ELECTRON
Use electrons to form an image.
Have a maximum resolution of 0.0002 micrometres.
Can be used to look as more organelles.
Maximum useful magnification x 1,500,000
Produce black and white images (often coloured by a computer).
What is the link between wavelength and resolution?
The shorter the wavelength, the higher the resolution.
The longer the wavelength, the lower the resolution.
Compare and contrast TEMs and SEMs.
TEMs
Use electromagnets to focus a beam of electrons which is transmitted through the specimen.
Denser parts of the specimen absorb more electrons which make them look darker on the image.
Give high resolution images so can see internal structure of organelles like chloroplasts.
2D images.
Specimen viewed in vacuum- only dead organisms.
Can only be used on thin specimens.
SEMs
Scan a beam of electrons across specimen, knocking off electrons from the specimen, which are gathered in a cathode ray tube to form an image.
Give lower resolution images than TEMs.
Images show the surface of the specimen and are 3D.
Can be used on thick specimens.
Can also only be used on non-living organisms.
Describe how you would prepare a microscope slide for a light microscope.
-Pipette a small drop of water onto the centre of the slide.
-Use tweezers to place a thin section of the specimen on top of the water drop.
-Add a drop of stain, highlighting parts of the cell.
-Add the cover slip, carefully tilting and lowering it so that it covers the specimen. Try not to trap any air bubbles- they will obstruct the view of the specimen.
What are microscope artefacts?
Things on the image that aren’t part of the specimen, usually made during preparation of specimen.
Especially common in electron microscopes because specimens need a lot of preparation (complex staining process) before viewing under a microscope.
What is the difference between temporary mounts and dry mounts?
Temporary- specimen is suspended in a drop of liquid on the slide.
Dry- not suspended in a drop of liquid on the slide.
What is the function of plasmids in a prokaryotic cell?
Small circle of DNA that contain genes for things like antibiotic resistance. Not always present in prokaryotic cells.
What is the function of the flagellum in a prokaryotic cell?
Long, relatively inflexible structure that helps the cell move. Not always present in prokaryotic cells.
What is the function of ribosomes in prokaryotic cells?
Site of protein synthesis, 70S, in cytoplasm.
What is the function of the cell wall in prokaryotic cells?
Made of murein, a glycoprotein. It supports the cell and prevents it from changing shape.
