2.1 cell structure Flashcards
-Define magnification?
The amount of times an image is larger then the original
Define resolution?
The minimum distance apart two objects can be in order for them to appear separate in the image
What are the types of microscopes?
Optical (light) microscope, scanning electron microscope, transmission electron microscope
Which type of microscope has the better resolution (electron or optical)?
Electron because the wavelength of an electron is shorter than the wavelength of light
Describe the structure of the nucleus?
-The nucleus is surrounded by the nuclear envelope, a double membrane.
-Nuclear pores enable movement of molecules into and out of the nucleus.
-The genetic material is found within nucleus, usually as chromatin.
-The nucleolus is a region within the nucleus that synthesises ribosomes
How does the structure of the RER relate to its function?
-contains ribosomes on its surface for protein synthesis
-The RER membranes spread extensively throughout the cell
Difference in structure between RER and SER
SER does not have ribosomes on outer surface whereas RER does.
What is the function of the smooth endoplasmic reticulum (SER)?
Synthesises and transports lipids
Describe the structure of mitochondria?
-Oval shaped
-Double membrane bound, inner membrane folded into cristae
-Contains jelly-like fluid called matrix
-Contains circular DNA and 70S ribosomes
Which important process occurs at mitochondria?
Aerobic respiration, producing ATP energy
What are lysosomes?
Vesicles from the Golgi body that contain digestive enzymes like proteases, lipases and lysozymes
What are the two types of ribosomes and where are they found?
-80S ribsomes are found in eukaryotic cells (in cytoplasm and on RER)
-70S ribosomes are found in prokaryotic cells, chloroplasts and mitochondria
Describe the structure of ribosomes?
Ribosomes contain two sub units. Each sub unit is made up of a ribosomal RNA molecule and a protein
Describe the structure of chloroplasts?
-Chloroplasts have a double membrane and contain a fluid called stroma. Within the chloroplast, thylakoids are arranged into interconnected stacks of grana. They also contain 70S ribosomes and circular DNA
Name the photosynthetic pigment in chloroplasts?
Chlorophyll
Which eukaryotic cells contain a cell wall?
-Plant cells
-algal cells
-fungal cells
Name the main constituent of plant cell walls?
Cellulose
In which type of cell are plasmodesmata found?
Plant and algal cells
Define the term eukaryotic cell?
DNA is contained in a nucleus, contains membrane-bound specialised organelles
Define the term prokaryotic cell?
DNA is free in cytoplasm, no membrane-bound organelles e.g. bacteria and archaea
Define a tissue?
A group of similar cells working together to perform a specific function
Define an organ?
A group of different tissues working together to carry out a specific function
Define an organ system?
A group of organs working in the body to carry out a complex function
What is the structure of the cell-surface membrane?
‘Fluid mosaic’ phospholipid bilayer with intrinsic and extrinsic proteins embedded
Describe the structure of the cell wall?
-Bacteria is made of the polysaccharide murein
-Plants is made of celluslose microfibrils, plasmodesmata allow molecules to pass between cells, middle lamella acts as a boundary between adjacent walls
Describe the structure of the cell vacuole in plants?
Surrounded by single membrane: tonoplast contains cell sap: mineral ions, water, enzymes, soluble pigments
State the role of plasmids in prokaryotes
-small ring of DNA that carries non-essential genes
-can be exchanged between bacterial cells via conjugation
State the role of flagella in prokaryotes?
Rotating tail propels (usually unicellular) organisms
What do both type of cells have?
-cell membrane
-cytoplasm
-Ribosomes (doesn’t count as organelle as not membrane bound)
Why are viruses referred to as ‘particles’ instead of ‘cells’
-Acellular and non-living:no cytoplasm
-cannot self reproduce
-no metabolism
Structure of a virus particle?
-linear genetic material (DNA or RNA) and viral enzymes e.g. reverse transcriptase
-surrounded by capsid (protein coat made of capsomeres)
-no cytoplasm
How do optical microscopes work?
- Lenses focus rays of light and magnify the view of a thin slice of specimen
- different structures absorb different amounts and wavelengths of light
- reflected light is transmitted to the observer via the objective lens and eye piece
How to prepare a temporary mount of tissue for an optical microscope?
- obtain thin section of tissue e.g. using ultratome or by maceration
- place plant tissue in a drop of water
- stain tissue on a slide to make structures visible
- Add coverslip using mounted needle at 45 degrees to avoid trapping air bubbles
Advantages of optical microscope?
-colour image
-can show living structures
-affordable apparatus
Negatives of optical microscope?
-2D image
-lower resolution than electron microscopes so cant see ultrastructure
How does a transmission electron microscope (TEM) work?
1.Pass a high energy beam of electrons through thin slice of specimen
2.More dense structures appear darker since they absorb more electrons
3. Focus image onto fluorescent screen or photographic plate using magnetic lenses
Advantages of using a TEM?
-electrons have shorter wavelength than light meaning higher resolution, so ultra structure visible
-high magnification (x 500000)
Negatives of using TEM?
-2D image
-requires a vacuum meaning cannot show living structures
-extensive preparation may introduce artefacts
-no colour image
How does a Scanning electron microscope (SEM) work?
- Focus a beam of electrons onto a specimen’s surface using electromagnetic lenses
- reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate.
Advantages of SEM?
-3D image
-electrons have shorter wavelength than light so higher resolution
Negatives of SEM?
-requires a vacuum so cannot show living structures
-no colour image
-only shows outer surface
State the equation to calculate the actual size of a structure form microscopy?
Image size (mm) x 1000/magnification = actual size
how to find magnification?
length of scale (mm) x 1000/scale value = magnification
Function of ribosomes
Protein synthesis (translation phase)
Function of chloroplasts
Site of photosynthesis
Function of Mitochondrion
Formation of ATP through aerobic respiration
Function of endoplasmic reticulum
smooth-lipid synthesis and transport
Rough-Protein synthesis and transport
Function of Golgi body
Chemical modification and packaging of proteins for exocytosis
Function of Centrioles
Produces spindle fibres during cell division
Function of lysosomes
Phagocytosis, autophagy, autolysis
Function of Cell wall
Provides strength and rigidity to the cell (preventing osmotic lysis)
Function of plant vacuole
Storage of amino acids and sugars, role in maintaining cell turgidity
Function of nucleus
contains cellular DNA which carries the genetic code for protein synthesis
Function of cell membranes
Act as a selectively permeable barrier
