Cells Flashcards
Defintion of eukaryotic cells
Have a distinct nucleus and membrane-bound organelles.
Describe the structure of the cell-surface membrane
7mm thick
Plasma membrane
Describe the function of the cell-surface membrane
Partially permeable membrane which controls exchange between the cell and its environment.
Describe the structure of the nucleus
Surrounded by 2 membranes known as the nuclear envelope. The envelope has nucelar pores. The nucelus contains a darker staining area, the nucleolus.
Describe the function of the nucleus
Contains genetic material as DNA and chromosomes. Produces mRNA and tRNA. The nucleolus manufactures rRNA. Nuclear pores allow mRNA and robosomes to leave the nucelus and nutrients and hormones to enter the nucleus.
Describe the structure of the mitochondria
Surrounded by 2 membranes called an envelope. 1-10 micrometers in length. The linear membrane is folded to form cristae which projects into the matrix. The matrix contains proteins, lipids, ribosomes and DNA so can producse own proteins.
Describe the function of the mitochondria
Aerobic respiration
Makes ATP
Describe the structure of rough and smooth endoplasmic reticulum
Ribosomes can be attached to the membranes = rough endoplasmic reticulum. No ribosomes = smooth endoplasmic reticulum.
Describe the function of smooth and rough endoplasmic reticulum
Rough- Provides a larger surface area for the synthesis of proteins and glycoproteins, and then transport these proteins through the cell. It makes the Golgi apparatus.
Smooth- Synthesises, stores and transports lipids and carbohydrates.
Describe the structure of the cell wall
Rigid cell wall made of polysaccharides, such as cellulose embedded in a matrix. The middle lamella is a thin layer marking the boundary between adjacent cell walls and cements cells together. Algae cell walls are made up of cellulose or glycoproteins or a mixture. In fungi, they are made of chitin.
Describe the function of a cell wall
Provides mechanical strength to the cell. Prevents the cell from bursting when water enters by osmosis. Freely permeable.
Describe the structure of a vacuole
Surrounded by a membrane called a tonoplast. Vacuole is fluid-filled.
Describe the function of a vacuole
Tonoplast controls the exchange of materials between the vacuole and the cytoplasm. Makes cells turgid for support.
Describe the structure of a chloroplast
Surrounded by 2 layers of membrane-envelope. Around 2-10 micrometers long. Stroma: a jelly-like substance inside. Membranes forming falttened sacs called thylakoid membranes = grana. Small starch grains and lipid droplets are present in the stroma.
Definition of ultrastructure
The detail of the inside of the cells, as revealed by the electron micrscope.
Definition of eukaryotes
These cells have a distinct nucelus and membrane-bound organelles.
Definition of division of labour
Each type of organelle has a specific role within the cell.
Describe the process of division of labour
- DNA in nucleus contains instructions to make proteins.
- Protein synthesised on ribosome.
- Protein transported through RER.
- Protein molecules are pinched off in vesicles and are transported towards the Golgi apparatus.
- Vesicles fuses with Golgi apparatus.
- Golgi apparatus process and packages protein molecules ready for release.
- Packaged protein molecules are pinched off in vesicles from the Golgi apparatus and are transported towards the plasma membrane.
- Vesicles fuses with plasma membarne.
- Protein leave by exocytosis.
Definition of a cell
The basic unit of living things
Definition of tissue
A group of similar or different cells work together for a specific function.
Definition of organ
Different tissues work together for a specific function
Definition of organ system
Different organs work together to support the whole system
Definition of an organism
Different systems work together to support the whole organism.
Rank of organisation
Organism>organ system>organ>tissue>cell
Describe the function of a cell wall in a bacterial cell
Physical barrier which prevents mechanical damage and osmotic lysis of the cell (made of murein).
Describe the function of a capsule of a bacterial cell
Protects bacteria
Describe the function of the flagellum in a bacterial cell
Locomotion
Describe the function of the ribosomes in a bacterial cell
Site of protein synthesis
Describe the function of circular DNA in a bacterial cell
Contains the genetic information for replication of the cell.
Describe the function of plasmids in a bacterial cell
Small circular peice of DNA which contains genes which help bacteria to survive adverse conditions, for example: location of antibiotic-resistant genes.
Describe the function of mesosome in a bacterial cell
Infolding of the plasma membrane creating a large surface area for attachment of enzymes. Location of respiration.
Describe the function of pili in a bacterial cell
Allows attachment of one bacyeri to another and the transfer of genetic information from one bacteria to another.
Definition of microscopy
How many times bigger the image is when compared to the object.
Definition of resolution
The minimum distnace apart that two objects can be in order for them to appear as separate items. The higher the resolution, the greater the clarity of the image.
Describe ow to prepare a slide for a light micrscope
- Add a drop of water to the slide.
- Obtain a thin section of the tissue (thin enough to let light pass through) and place on the slide / float on the drop of wtare.
- Stain with / add iodine in potassium iodide.
- Lower cover slip using mounted needle, this is to prevent air bubbles forming to obscure view of image.
- Press cover slip down firmly so thin layer of cells to allow light to pass through.
Why is staining the specimen important?
The nucleus and cytoplasm are visible. There is an increased contrast between the cytoplasm and the surrounding solution and between the cytoplasm and the nucleus. This allows identification of the nucleus and cytoplasm.
Describe how an electron micrscope forms an image
Electron beam passes through a very thin section of the sample. Electrons cannot pass through thr stained parts of the nucleus, so this appears darker on the screen. Electrons pass through the cytoplasm and cause light emission on the screen.
Why does an electron microscope have a higher resolution than a light microscope?
- Electrons have a shorter wavelength than light. Wavelength of light is 400 nm and the wavelength of electrons is 1nm.
- Electrons can pass between two objects that are extremely close together.
- Electron microscopes can distinguish between two extremely close objects.
- The maximum resolving power is 0.1-0.2nm.
- A smaller distance, the higher the resolution.
The features of TEM
TEM- Transmission electron microscpes
Can see internal structures of the cell
Image is 2D
Resolution is 0.1nm
The features of SEM
SEM- Scanning electron microscopes
Image is 3D
Resolution is 20nm
Compare electron and light microscope
- Electron microscopes use electron beams; light micrscopes uses light rays.
- Electron micrscopes have a greater resolution than a light micrscope.
- Electron microscopes show smaller organelles, light microscopes shows larger organelles.
- Electron microscopes show smaller structures inside cells, light microscopes show larger structures inside cells.
- Electron microscopes use dead specimens, light microscopes use living specimens.
- Electron microscopes require a thinner specimen, light microscopes require a thicker specimen.
- Electron microscopes have a more complex slide preparation, light microscopes have a simpler slide preparation.
Compare SEM and TEM
- SEM have a lower resolution, TEM have a higher resolution.
- SEM produces an image of the surface of the specimen, TEM shows a picture of the internal structures of the cell.
- SEM produces a 3D image, TEM produces a 2D image.
- SEM requires a thicker specimen, TEM requires a thinner specimen.
Advantages and disadvantages of light microscopes
ADV- Live specimens
DIS- Poor resolution. Need a thin specimen
Advantages and disadvantages of TEM
ADV- High resolution
DIS- Dead specimen only as it is in a vacuum. Needs very thin specimen. Difficulty preparing specimen can limit resolution. High energy electron beam may destroy specimen.Requires complex staining processes. Artefcats risen from preparation that are not part of the natural specimen.
Advantages and disadvantages of SEM
ADV- High resolution. 3D image. Can be a thick specimen.
DIS- As with TEM except that a thick specimen may be used as the electrons scatter rather than pass through.
What are artefacts?
Structures that look different to how they orginally did in the whole cell.
What is the equation for magnification?
Magnification = image size / actual size
What is an eyepiece graticule?
An eyepiece lens with a scale etched on the glass. This scale has no units, so it is an arbitrary scale.
What is a stage micrometer?
This is a glass slide with a scale of known dimensions on it. 1 division on the stage micrometer is 100 micrometers.
Describe how to use a stage micrometer to calibrate the eyepiece graticule to determine the actual length of an object
- Place the stage micrometer onto the stage of the microscope.
- Focus the microscope so the stage micrometer ruler becomes visible.
- Line up the eyepiece graticule scale with the stage micrometer ruler.
- Determine how many small divisions (eyepiece units) on the eyepiece grtaicule there are between a single division on the stage micrometer (a length of 100 micrometers).
- Divide 100 micrometers by the number of the eyepiece units to determine the length of a single eyepiece unit (division) of the eyepiece graticule.
Describe how to use the calibrated eyepiece graticule to determine the actual length of an object
- Remove the stage micrometer slide and replace with the slide containing the specimen being studied.
- Use the eyepiece graticule scale to find how many eyepiece units long the object is.
- Multiply the number of eyepiece units (divisions) by the calibrated length of a single division to determine the actual length of the object.
Describe the method used to separate cell components
- Chop up fresh tissue in ice cold, isotonic buffer solution. The ice stops enzyme activity so organelles are not digested. The solution is isotonic so stops osmotic damage to the organelle and the buffer maintains a constant pH so enzymes are not digested.
- Put the chopped tissue into the blender or homogeniser to break open the cells to separate organelles. The fluid produced is called the cell homogenate.
- Filter the homogenate to remove larger debris.
- Pour the mixture in to the tubes and spin very quickly in a centrifuge. This is ultracentrifugation. The organelles separated based on mass and density.
- The heaviest organelles, the nuceli, are forced to the bottom and form a sediment or pellet. The fluid left at the top is removed leaving just the sediment of the nuclei. This fluid is called the supernatant.
- The supernatant may then be spun again at a higher speed to produce a sediment containing mitochondria and chloroplasts, and at an even higher speed for other organelles (in order; lysosomes, RER, plasma membrane, SER, ribosomes). Most dense to least dense.
Why is cell fractionation carried out?
So scientists can study the function and structure of organelles.
