2. Cell Structure Flashcards
nucleus structure
* contains …
* region called…
* surrounded by ..
- contains chromosomes within nucleoplasm
- contains central region called nucleolus
- surrounded by nuclear envelope (double membrane) w nuclear pores to let molecules in & out
mitochondria structure
* double ..
* inner…
* DNA…
* site of…
- double membrane
- inner membrane folded forming cristae
- short, circular DNA (no proteins) (mtDNA)
- site of AEROBIC resp
- resp is chem reaction which prod ATP (releases energy)
- fluid inside called matrix
ribosomes have no
membrane
which organisms have: cellulose
- plants
- algae
which organisms have: muerin
prokaryotes
which organisms have: chitin
fungi
what is the nuclear envelope
double membrane surrounding nucleus w nuclear pores to let molecules in & out
cytoplasm:
where chem reactions take place
ribosomes:
where amino acids joined together to make proteins
- have no membranes
- site of translation
rough endoplasmic rectilum
- has ribosomes on surface -> involved in protein synthesis
- proteins folded up inside the RER
smooth endoplasmic rectilum
- synthesis and storage of molecules
- eg. sterols, steroids, lipids
golgi apparatus and golgi vesicles
- modifies proteins
- stores proteins
- packages proteins into vesicles
- transports vesicles to cell surface
- modifies triglycerides (into chylomicrons)
lysosomes
a vesicle that contains hydrolytic enzymes (lysozymes) used to digest molecules
chloroplast:
- chlorophyll absorb light for photosynthesis to prod. carbohydrates
- has double memb. where:
- thylakoid membranes can form grana stacks, linked by lamellae
- ctDNA fluid is called stroma, has ribosomes
cell wall; in each cell type
for strength and support
* cellulose - plant cells
* meurin - bacteria
* chitin - fungi
vacuole
- tonoplast - membrane surrounding vacuole
- when vacuole full of fluid, cell turgid
- temp food store containing sugars and amino acids
- contains pigments
…… produces vesicles containing newly synthesised proteins:
RER
…. the site of steroid production
SER
what produces lysosomes
golgi apparatus
Explain the advantages and limitations of using a transmission electron microscope to study cells. (6)
1 TEM uses (beam of) electrons;
2 These have short wavelength;
3 Allow high resolution
4 Electrons scattered (by molecules in air);
5 Vacuum established;
6 Cannot examine living cells;
7 Lots of preparation/procedures used in preparing specimens/ fixing/staining/sectioning;
8 May alter appearance/result in artefacts;
Describe how the structures of starch and cellulose molecules are related to their functions. (5)
Starch (max 3)
1. Helical so compact;
2. insoluble so osmotically inactive
3. Branched so glucose is (easily) released for respiration;
4. Large (molecule) so cannot leave cell
Cellulose (max 3)
5. Long, straight/unbranched chains of β glucose;
6. Joined by hydrogen bonding;
7. To form fibrils;
8. Provides strength;
Explain why the diffusion of chloride ions involves a membrane protein and the diffusion of oxygen does not. (5)
- Chloride ions are polar;
- Cannot cross (lipid) bilayer
- Chloride ions transported by facilitated diffusion
- Oxygen non-polar;
- Oxygen can diffuse across bilayer;
define magnification
how much bigger the image is compared to specimen
resolution
minimum distance apart that two objects can be in order to appear as seperate items
desc. procedure to prepare a slide
- add drop of water to slide
- remove thin section of tissue & place it flat on slide
- add 1 drop of iodine dissolved in KI solution to stain sample (only for plant cells)
- lower coversplip on top using mounting needle
microscopy
why tissue needs to be thin
- thin section allows more light to penetrate
- allows a single layer of cells to be viewed
microscopy
why should you push down on coverslip hard but not push sideways
- down hard to squash tissue and get a single layer of cells
- sideways will cause cells to roll together
microscopy
describe how the length of a cell can be estimated (optical microscope)
- use stage micrometer to calibrate size of eyepiece graticule
- measure length of plant cell with an eyepiece graticule
why are ETM used to view cells
- they have high resolution
- bcs electrons have shorter wavelength than light
- allows you to view internal structures/organelles of a cell
why do ETM have higher resolution than optical?
electrons have shorter wavelength than light
Name two structures in a eukaryotic cell that cannot be identified using an optical microscope
- Mitochondrion.
- Ribosome.
- endoplasmic reticulum
- lysosome
- cell surface membrane
Name the organelles in order of density.
- Nuclei.
- Chloroplasts (if carrying out cell fractionation of plant tissue)
- Mitochondria.
- Lysosomes.
- Endoplasmic reticulum.
- Ribosomes.
Principles of using TEM microscope. (4)
how does it work
- Electrons pass through thin specimen.
- Denser parts absorb more electrons
- denser parts appear darker.
- Electrons have a short wavelength, so give high resolution.
Limitations of using TEM microscope. (5)
- cannot look at living material.
- Specimen must be very thin.
- artefacts present.
- Long preparation time.
- Image not in 3D
Advantage of TEM over SEM.
- Higher resolution
- allows internal structures within cells to be seen.
Advantage of SEM over TEM.
- Thin sections do not need to be prepared.
- Show surface of specimen.
- Can have 3D images
How many um in a mm?
1mm = 1000 um.
Microscopy.
How to use a scale bar?
- Measure scale bar using a ruler in mm.
- Convert to micrometres - use value as image size.
- The value written underneath the scale bar is actual size.
- Use both to work out magnification.
What is meant by cell fractionation and why do we use it?
- Separating out the contents of the cell into different fractions.
- separating out the different organelles by density.
- Allows to study individual organelles.
What is homogenization?
Using a blender to break open the cell membrane to release all the organelles inside.
Which microscopes use a magnet to focus the beam of Electrons
TEM and SEM
Give the resolutions of the microscopes
SEM = 20 nm
TEM = 0 .1nm
Optical = 0.2 um
Differentiate between channel proteins and carrier proteins.
- Channel proteins allow the passage of molecules, some are gated (open in response to stimulus).
- Carrier proteins require a concentration difference across the membrane and must bind to the molecule they transport.
describe how carrier proteins transport substances (4)
- substance binds to specific binding site on carrier protein
- causes conformational change
- allows molecules to be taken across membrane to other side
- carrier returns to original shape
equation for rate of diffusion
con m x SA / length of diff pathway
covert from mm to um
convert from um to nm
/ 1000
/ 1000
cell membranes
there is no cholesterol in..
prokaryotes membranes
Cholesterol molecules sit in between the phospholipids, preventing them from
packing too closely together when temperatures are low; this prevents membranes from freezing and fracturing.
Membranes become less fluid when there is:
- inc. proportion of saturated fatty acid chains -> chains pack together tightly -> there is a high number of IMF between the chains
- A lower temperature as the molecules have less energy and therefore are not moving as freely which causes the structure to be more closely packed
Membranes become more fluid when there is:
- inc. proportion of unsaturated fatty acid chains -> chains are bent -> the chains less tightly packed together-> less intermolecular forces
- At higher temps, molecules have more energy and therefore move more freely, increasing membrane fluidity
Factors that affect diffusion
- Steepness of concentration gradient
- temperature
- surface area
- Properties of molecules of ions e.g.
large or small : smaller molecules will diffuse faster as less energy required to move molecule
polar / non-polar; non-polar diffuse more quickly as they are soluble in nonpolar phospholipid bilayer
channel and carrier proteins
are highly specific.
they only let one type of molecule or ion to pass through
channel proteins are …. filled pores
channel proteins are water-filled pores
They allow charged substances to diffuse through cell membrane
What does it mean when a cell is in a hypertonic environment
the solution has a higher solute concentration than the inside of the cell
* thr4 net movement of water out of the cell
In plant cells water enters
The vacuole
what is the protoplast
the liviving part of the cell inside the cell wall
plasmolysis is when:
the protoplast shrinks away from the cell wall
- because the volume of the protoplast decreases as water leaves the cell
cell walls are …. perm…
fully permeable
What happens when a plant cell is placed in solution with higher water potential (6)
water enters cell …. cell fully inflated…
- Water enters cell through partially permeable membrane by osmosis
- volume of cell increases
- portoplast expands & pushes against cell wall
- cell wall withstands increased pressure created
- pressure increases until cell is rigid and firm
- cell is fully inflated with water and no more can enter
osmosis practical
how to find the concentration of sucrose inside the potato cylinders
when line crosses the x axis of graph of % mass change against concentration
Describe the main ideas of the cell theory (3)
- All living organisms are made up of one or more cells
- cells are the basic functional unit in living organisms
- New cells are produced from pre-existing cells
Cell theory is a
Unifying concept in biology
what is the liquid found in a chloroplast
Stroma
Describe the function of chloroplasts (2)
- Absorb light
- Perform photosynthesis
- Produce carbohydrates
Explain why the epithelial cells of the small intestine would contain large numbers of mitochondria: (3)
- mitochondria produce ATP
- which is required for active transport
- during absorption of digested food
Prokaryotic cells are much smaller than eukaryotic cells. They also differ from eukaryotic cells in having:
- cytoplasm that lacks membrane-bound organelles
- smaller ribosomes
- no nucleus; instead they have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins
- a cell wall that contains murein, a glycoprotein
In addition, many prokaryotic cells have:
- one or more plasmids
- a capsule surrounding the cell
- one or more flagella.
Virus structure:
- A nucleic acid core (their genomes are either DNA or RNA, and can be single or double-stranded)
- A protein coat called a ‘capsid’
eukaryotic structures that can’t be seen with optical microscope
- mitochondria
- ribosomes
- endoplasmic reticulum
- lysosome
- cell surface membrane
describe how RER is involved in production of enzymes
- contains ribosomes
- to make proteins (which enzyme is)
contrast structure of a bacterial cell and the structure of a human cell (5)
- bacterial cell has circular loops of DNA but humans have linear DNA
- bacterial cell is smaller but human cells are larger
- bacterial cells don’t have membrane bound organelles but human cells
- do bacterial cells have plasmids free in cytoplasm but human cells don’t
- Bacterial cells have cell wall but human cells don’t
- Bacterial DNA is not associated with proteins
- bacterial cells have slime capsule
- bacteria lacks nucleus
- bacterial cells have 70S ribosomes but human cells have a 80S ribosomes
Write a flow chart to describe binary fisson
- Circular DNA and plasmids replicate
- the circular DNA’s get pulled to opposite ends of cell and attaches to cell membrane
- plasmids move randomly by diffusion bacterial cell grows so cell elongates further apart from each other
- cell membrane pinches inwards in the middle of the cell so the cytoplasm divides
- new cells wall forms producing 2 daughter cells
Write a flow chart to describe replication of viruses
- virus attaches to host cell using attatchment proteins
- nucleic acid gets injected into host cell
- host cell transcribes and translates viral genes
- these proteins form new virus particles made
- too many viruses ➜ cell lysis
- viruses escape and infect more cells
- host cell destroyed
what is a capsid
- The capsid is the protective protein coat that surrounds the viral genetic material.
- It helps to protect the virus from the host’s immune system and to deliver the viral genetic material into the host cell.
give a function of glycoproteins
cell recognition
why can’t an optical microscope see plasma membrane
- resolution is not high enough
- as light has a longer wavelength
Describe how lactose is made and how in the cell it’s attatched to a polypeptide to form a glycoprotein and transported to the cell surface
- glucose and galactose
- joined by condensation reaction
- joined by a glycosidic bond
- added to polypeptide in golgi apparatus
- transported to cell surface in a vesicle
describe replication process of bacterial cells (6 marks)
- Binary fission
- circular DNA and plasmids replicate
- circular DNA attaches to opposite ends of cell membrane
- bacterial cell grows
- cell membrane pinches inwards in the middle of the cell
- cytoplasm divides to form 2 daughter cells each has variable number of plasmids
- cell wall is formed around each daughter’s cell
Describe how you would use a microscope to find the mean diameter of triglyceride droplets on a slide. (3)
- Place a stage micrometre on the stage.
- Calibrate the eye piece graticule using the stage micrometre.
- Measure how many eye piece graticules is one bile droplet
- Repeat measurements from each concentration to find mean diameter.
Give the two types of molecules from which a ribosome is made
- ribosomal RNA
- ribosomal protein
Structures that are found in bacteria but not plant cells: (2)
- circular DNA
- meurin cell wall
- smaller ribosomes (70S)
Explain how a foetus is protected from pathogens that infect its mother during its pregnancy (3)
- antibodies (from mother) are complementary/bind specifically;
- To pathogens/antigens crossing the placenta;
- Giving passive immunity (in fetus)
Explain how giving children more than one jab develops good immunity against tetanus (2)
- more memory cells produced
- more rapid production of antibodies (on further infection)
Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells. (6)
- TEM use electrons and optical use light;
- TEM allows a greater resolution;
- (So with TEM) smaller organelles / named cell structure can be observed
- TEM view only dead / dehydrated specimens and optical (can) view live specimens;
- TEM does not show colour and optical (can);
- TEM requires thinner specimens;
- TEM requires a more complex/time consuming preparation;
- TEM focuses using magnets and optical uses (glass) lenses;
Beetroot pigment practical
Why was it important to control the volume of water?
- if the volume is too high then the concentration of the pigment will be lower
- makes results comparable
What 2 organelles are needed for antibody production?
- rER / ribosomes
- golgi apparatus
Explain why the potato increased in length: (2)
- water moves in down a WP gradient
- cells become turgid and elongate
Suggest and explain how two environmental variables could be changed to increase the growth rate of these cells. (4)
- Increased (concentration of) glucose;
- Increased respiration;
.. - Increased (concentration of) oxygen;
- Increased respiration;
.. - Increased (concentration of) nucleotides;
- Increased DNA synthesis;
