2.1.1 - Cell Structure Flashcards
How does a light microscope work?
It uses light to form an image. Light that passes through or reflects from the surface of the specimen is seen.
What images are produced by light microscopes?
- Poor resolution due to the long wavelength of light (200nm)
- Low magnification (2000x)
- Colour image
- 2D
Which specimens can be examined by light microscopes?
Living and non-living specimens
How does a transmission electron microscope work?
It uses electrons to form an image. The electrons that pass through the specimen are detected.
What images are produced by transmission electron microscopes?
- High magnification (1000000x)
- High resolution due to short wavelength of electrons (0.2nm)
- Black and white
- 2D
Which specimens can be examined by transmission electron microscopes?
Only non-living specimens as the microscope must be in a vacuum so the air doesn’t absorb the electrons.
How does a scanning electron microscope work?
It uses electrons to form an image. Electrons that are reflected from the surface on the specimen are detected.
What images are produced by scanning electron microscopes?
- High magnification (1000000x)
- High resolution due to short wavelength of electrons (3-20nm)
- Black and white
- 3D
Which specimens can be examined by scanning electron microscopes?
Only non-living specimens as the microscope must be in a vacuum so the air doesn’t absorb the electrons.
How does a laser scanning microscope work?
It uses a laser beam to scan an object pixel by pixel creating an image of the reflected photon.
What images are produced by laser scanning confocal microscopes?
- High resolution
- 2D and 3D images
- Black and white/computer generated colour
What are dry mounts?
When thin slices or whole specimens are viewed with just the coverslip placed on top
What are wet mounts?
When water is added to the specimen before lowering the coverslip with a mounted needle to prevent air bubbles from forming. This is used for aquatic organisms.
What are squash slides?
Wet mounts which you then push down on the coverslip to squash the sample to ensure you have a thin layer to enable light to pass through. This is used for a root tip to view the chromosomes in mitosis.
What are smear slides?
When you use the edge of another slide to smear the sample across the slide to create a smooth, thin and even coated specimen. A cover slip is placed on top after smearing. This is used when examining blood cells in a blood sample.
How do you calibrate an eye piece graticule?
- Line up the stage micrometer and eyepiece graticule whilst looking through the eyepiece
- Count how many divisions on the eyepiece graticule fit into one division on the micrometer scale
- Each division on the micrometer is 10μm so this can be used to calculate what one division on the eyepiece graticule is
Why are stains used in microscopy?
- To make cells more visible
- Increase contrast
- Identify different cell components
What is the formula for magnification?
Magnification = image size/object size
What is magnification?
The number of times greater the size of the image is than the size of the real object
What is resolution?
The ability to distinguish between two objects that are very close together. A higher resolution means more detail.
What is the structure of the nucleus?
- Nuclear envelope which is a double membrane that has nuclear pores to control exchange between the nucleus and cytoplasm
- Nucleoplasm which is a granular jelly like material
- Chromosomes which are protein bound linear DNA
- Nucleolus which is a smaller sphere inside which is the site of rNA production and makes ribosomes
What is the function of the nucleus?
- Site of DNA replication and transcription
- Contains the genetic code for each cell
- Site of ribosomal synthesis
What is the structure of flagella?
Long whip like structure
What is the function of flagella?
Involved in mobility and sometimes as sensory organelle for chemical stimuli
What is the structure of cilia?
Short hair like projections out of cells
What is the function of cilia?
- Can be mobile or stationary
- Mobile cilia help move substances in a sweeping motion
- Stationary cilia are important in sensory organs such as the nose
What is the structure of centrioles?
- Made of microtubules
- Occur in pairs to form a centrosome
What is the function of centrioles?
Involved in the production of spindle fibres and organisation of chromosomes in cell division
What is the structure of the rough endoplasmic reticulum?
- Has folded membranes called cisternae
- Covered in ribosomes
What is the function of the rough endoplasmic reticulum?
Site of protein modification and protein synthesis
What is the structure of the smooth endoplasmic reticulum?
Has folded membranes called cisternae
What is the function of the smooth endoplasmic reticulum?
- Synthesises lipids, steroids and some hormones
- Synthesises, stores and transports carbohydrates
What is the structure of the Golgi apparatus?
- Folded membranes making cisternae
- Secretory vesicles pinch off from the cisternae
What is the function of the Golgi apparatus?
- Makes lysosomes
- Adds carbohydrates to proteins to form glycoproteins
- Transport, modify and store lipids
- Finished products are transported to cell surface in Golgi vesicles where they fuse with the membrane and contents are released
What is the structure of lysosomes?
Bags of digestive enzymes
What is the function of lysosomes?
- Hydrolyse phagocytic cells
- Break down dead cells
- Exocytosis - release enzymes to outside of cell to destroy material
- Digest worn out organelles for reuse of materials
What is the structure of mitrochondria?
- Double membrane
- Inner membrane highly folded into cristae
- Fluid centre called the mitochondrial matrix
- Loop of mitochondrial DNA
What is the function of mitochondria?
- Site of aerobic respiration
- Site of ATP production
- Contains DNA to code for enzymes needed in respiration
What is the structure of ribosomes?
- Small made up of two sub units of protein and rRNA
- 80S is a large ribosome found in eukaryotic cells (25nm)
- 70S is a smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts
What is the function of ribosomes?
Site of protein synthesis
What is the structure of chloroplasts?
- Surrounded by a double membrane
- Contains thylakoids which are folded membranes embedded with pigment arranged in stacks called grana
- Fluid filled stroma contains enzymes for photosynthesis
- Found in plants
What is the function of chloroplasts?
Site of photosynthesis
What is the structure of the cell wall?
- Found in plant and fungi cells
- In plants it is made of microfibrils of the cellulose polymer
- In fungi it is made of chitin which is a nitrogen containing polysaccharide
What is the function of the cell wall?
Provides structural strength to the cell
What is the structure of the plasma membrane?
- Found in all cells
- Phospholipid bilayer with molecules embedded within and attached on the outside such as proteins, carbohydrates and cholesterol
What is the function of the plasma membrane?
Controls the exchange between the cell and its environment
How are proteins produced and secreted?
- Polypeptide chains are synthesised on the RER
- These polypeptide chains move to the cisternae in the RER and are packaged into vesicles to be sent to the Golgi apparatus via the cytoskeleton
- In the Golgi apparatus the proteins are modified and packaged into vesicles
- The secretory vesicles carry the proteins to the cell surface membrane where it fuses and releases the protein by exocytosis
What are the 3 main functions of the cytoskeleton?
- Provides mechanical strength to cells
- Aids transport within cells
- Enables cell movement
What are the key differences between prokaryotic and eukaryotic cells?
- Prokaryotic cells are much smaller
- Prokaryotic cells have no membrane bound organelles
- Prokaryotic cells have smaller ribosomes
- DNA is not contained within the nucleus in prokaryotic cells
- Prokaryotic cell wall contains peptidoglycan
- Prokaryotic cells may also contain plasmids, flagella and a capsule around the cell
