3.1.2 CELLS AND THEIR STRUCTURE
EQ: The cell is adapted for three functions listen below. Use the diagram to explain how this cell is adapted for each of these functions. Use a different feature in the diagram for each of your answers. (i) The active transport of substances from the cell into the blood (2 marks) (ii) (Describe how the RER is involved in the production of enzymes) the synthesis of enzymes (2 marks) (ignore references to Golgi or rough ER) (iii) rapid diffusion of substances from the lumen of the gut into the cytoplasm (1 mark)
(i) Mitochondria aerobically respire to produce ATP for active transport against gradient (ii) Ribosomes make proteins / enzymes Enzyme are proteins (iii) Microvilli increase surface area (name structure, function and relate to question)
State three features that indicate a cell is eukaryotic:
- Nucleus - Membrane bound organelles (accept SER, RER, vesicle) - Ribosomes larger (80S)
What sort of microscope would the scientists use to take photographs of mitochondria? Give one reason for your answer.
- TEM; need high resolution to see structure of mitochondria
EQ: The student cut thin sections of tissue to view with an optical microscope. Explain why it was important that the sections were thin. (2 MARKS)
1. To allow (more) light through (accept transparent) 2. A single / few layers of cells to be viewed.
What is the size of eukaryotic cells?
10-100 micrometers
What is one mm in micrometers?
1000
What is the ribosomes in prokaryotic cells?
70s
What is the ribosomes in eukaryotic cells?
80s
EQ: Give one piece of evidence that supports the theory that mitochondria evolved from prokaryotic cells.
Has circular DNA and smaller 70S ribosomes (no introns or histones)
EQ: Describe the levels of cellular organisation that include the epithelial cell shown.
The levels of cellular organisation that include the epithilial cell are - speciliased epithelial cells make up epithilial tissue - epithelial tissue works together with other tissue to form the organ of the small intestine - the small intestine combines together with other organs such as the stomach to make the digestive system
Label this algal cell:
1. Cell membrane 2. Cell wall 3. Chloroplast 4. Rough endoplasmic reticulum 5. Smooth endoplasmic reticulum 6. Vacuole 7. Cytoplasm 8. Golgi apparatus 9. Lysosome 10. Nuclear envelop 11. Nucleus 12. Nucleolus 13. Ribosome 14. Mitochondria
Label this prokaryotic cell.
1. Cell wall (murein) 2. Smaller ribosome 3. Cytoplasm 4. Flagellum 5. Capsule 6. Plasmid 7. Circular DNA 8. Cell-surface membrane
Label this plant cell:
1. Chloroplast 2. Cytoplasm 3. Rough endoplasmic reticulum 4. Smooth endoplasmic reticulum 5. Glogi apparatus 6. Vacuole 7. Cell wall 8. Cell membrane 9. Nuclear envelope 10. Nucleus 11. Nucleolus 12. Lysosome 13. Mitochondria 14. Ribosome
EQ: Explain why lungs can be considered to be an organ.
An organ is a group of tissues working together to enable gas exchange * (explain: relate to the question)
Why do we place cells in a buffered solution before fractionation and ultracentrifugation?
Buffered keeps pH constant so enzymes dont denature
EQ: How do plasmids speed up the process of evolving antibiotic resistance in prokaryotic cells?
Can be passed between bacteria
What are eukaryotes?
Cells with a nucleus
Name one structure present in animals cells that isn't present in plant cells:
Centriole (glycogen granule)
What organelle is found in plant cells that contains inner membranes arranged in stacks?
Chloroplasts
Contrast the structure and the function of chloroplasts and mitochondria and give two differences.
Chloroplasts contain thylakoid membranes wheres mitochondria contain folded inner-membrane that forms structures called cristae. Chloroplasts are the site of photosynthesis whereas mitochondria are the site of aerobic respiration.
Why do we place cells in a cold solution before fractionation and ultracentrifugation?
Cold reduces enzyme activity so organelles arent broken down (digested)
EQ: Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells (5 MARKS)
Comparisons: - DNA in mitochondria and chloroplasts similar to DNA in prokaryotes - DNA nucleotide structure is identical - Nucleotides joined by phosphodiester bond Contrasts: - Eukaryotes have linear DNA, prokaryotes have circular loop of DNA - Eukaryotes DNA contain introns, prokaryotic DNA doesn't contain introns - Eukaryotic DNA is longer - Eukaryote DNA is folded around histones, prokaryotic DNA isn't
Describe the function of the nucleus.
Contains DNA and controls the cells activity through transcription on mRNA
EQ: If a leaf sample were viewed under a electron microscope, ribosomes and cell membranes could be viewed clearly. Explain why. (1 MARK)
Electron microscopes have higher resolution because electrons have have shorter wavelength than light to see internal organelles.
Give an example of an extracellular protein secreted in exocytosis:
Enzyme, glycoprotein
EQ: Describe the function of a chloroplast and the structural features that enable it to carry out these functions (5 MARKS)
FUNCTION: - absorb light - for photosynthesis - to produce carbohydrates / sugars / lipids / proteins STRUCTURAL ADAPTATIONS: - contains chlorophyll - contains thylakoid membranes / grana to maximise surface area being exposed to light - contains starch granules as food storage
Why do we place cells in a isotonic solution before fractionation and ultracentrifugation?
Isotonic so water doesn't move in/out of organelles by osmosis so they dont burst / shrivel
EQ: Describe how the RER is involved in the production of enzymes. (2 MARKS)
It has ribosomes to make protein (which an enzyme is)
What are golgi vesicles?
Made by Golgi apparatus, store and transport proteins and lipids out of the cell (exocytosis)
What are things eukaryotes have that prokaryotes dont?
Membrane bound organelles (no mitochondria or chloroplasts, no Golgi apparatus, no rough / smooth endoplasmic reticulum)
EQ: The proteins embedded in the membranes of vesicles have different functions. COPI and COPII proteins are known as 'address proteins' Vesicles that transport materials from the Golgi to the rough endoplasmic reticulum (RER) are coated in COPI proteins. Vesicles that transport materials to the Golgi from the RER are coated in COPII proteins Suggest how these proteins ensure that a vesicle is transported to the correct target organelle. (2 MARKS)
Receptor found only on target organelle and protein has a specific shape (shape of receptor and address protein are complementary)
Nuclear pore complexes (NPCs) control the passage of substances in and out of the nucleus. In the scientists study, cells from mutant plants with reduced npc function were also centrifuged. The cells from mutant plants produced a smaller pellet containing ribosomes, compared to cells from non-mutant plants. Explain why.
Ribosomes are made in the nucleolus. The nucleolus is found within the nucleus. If there was reduced function of the nuclear pore complexes, then fewer ribosomes could pass through the nuclear pore into the cytoplasm.
What are prokaryotes?
Single-celled organism whose DNA is suspended freely in cytoplasm, smaller than eukaryotes
EQ: State the contents and function of the mitochondrial matrix (2 MARKS)
The contents of the mitochondrial matrix are - DNA OR proteins OR ribosomes OR lipids The function of the mitochondrial matrix is: - To synthesise the proteins required in the mitochondrion - To store substrates required for protein synthesis
EQ: H. pylori cells produce an enzyme that neutralises acid. Suggest one advantage to the H. pylori of producing this enzyme
To stop / reduce them being damaged by stomach acid
Suggest one stage during the secretion of Protein that requires energy.
Transport vesicles to cell surface membrane, exocytosis
What is a tissue?
a group of identical cells joined & working together to preform a specific function
What is a flagellum? (prokaryotic cells only).
aids movement due to rigid corkscrew shape and it rotates to move cell
Give examples of eukaryotes.
animals, plants, fungi
Give examples of prokaryotes.
bacteria, archae
What does a plant cell have that an animal cell doesn't?
cellulose cell wall, chloroplast and a large permanent vacuole
What is the function of a nuclear envelope?
controls entry and exit of materials in and out of nucleus. contains nuclear pores that allow movement of substances in or out of the nucleus e.g. mRNA to move between the nucleus and cytoplasm
What is a specialised cell?
differentiated cell that has evolved to carry out a specific function with adaptation specific to its function
What is resolution?
minimum distance between two objects for them to appear as separate objects
A second centrifuge tube was spun at a higher speed than the first to obtain the sample
mitochondria is less dense than nucleus (organelle in first pellet)
Describe fungi
no chloroplasts, cell wall made of chitin
What is cell fractionation?
process by which cells are broken up and the different components they contain (organelles) are separated out.
Describe the function of a mitochondria.
releases energy by producing ATP through aerobic respiration
What are artefacts?
things that result from the way the specimen is prepared; not part of the natural specimen.
What is resolution limited by?
wavelength of radiation used e.g. light has longer wavelength than electron so lower
What is an organ?
group of organised different tissues; joined and working together to perform a specific function
What is an organ system?
group of organised organs; working together to perform a specific function
What is circular DNA (Nucleiod)? (prokaryotic cells only).
has genetic information for replication of bacterial cells
Describe a technique that could be used to break open the cells.
homogenise
What is a cell capsule? (prokaryotic cells only).
layer of slime protects bacterium from other cells & helps bacteria stick together for protection
How do you measure magnification?
magnification = size of image / size of real object
What does the nucleolus do?
makes ribosomes which are made up of proteins and ribosomal RNA (synthesis of RNA)
Name the order of mass/density in which cell fractionation and ultracentrifugation creates pellets in:
nuclei → chloroplasts → mitochondria → lysosomes → endoplasmic reticulum → ribosomes
EQ: Name the structure where the polypeptide chain of an enzyme would be synthesized (1 MARK):
rough endoplasmic reticulum / ribosomes
What are plasmids? (prokaryotic cells only).
small, circular molecule of DNA that has genes aiding in survival in adverse conditions
What is magnification?
the degree to which an object has been made bigger in an image compared to the real size, measured by magnification = size of image / size of real object
Label the chloroplast diagram
this includes the Thylakoids Stroma Granum
Describe the limitations of an optical microscope.
- 2D image - Only used on thin specimens - much Lower magnification & resolution; cant see internal structures of organelles or organelles smaller than 200nm e.g. ribosomes
EQ: Name the parts labelled X and Y.
- 80s large ribosomes - Membrane / cisterna
An outbreak of cholera occurred in London in 1849. The graph shows the relationship between the number of deaths from cholera and the height at which people lived above sea level. Describe the relationship between the number of deaths from cholera and the height at which people lived above sea level. (2 MARKS)
- As height increases, the number of deaths decrease (inversely proportional / negative correlation) - Correct reference to increase / decrease at 14-30m;
Describe the advantages of an optical microscope.
- Can see living organisms (benefits; cheap, easy)
EQ: Identify the structures labelled A-C
- Cell wall (glycoprotein murein) - Ribosomes - DNA / genetic material
EQ: Describe how the cells in a multicellular organism are organized: ( 5 marks)
- Cells differentiated / specifliased - Group of cells form tissue - Group of tissues form organs - Group of organs form organ systems - Group of cells, tissues, organs and organ systems work together
Describe the structure and function of the cell vacuole (plants).
- Contains cell sap: weak solution of sugars and salts. - Surrounding membrane is called tonoplast - keeps cell turgid; Maintains pressure in cell (stop wilting) - Stores/isolates unwanted chemicals in the cell e.g. waste
Describe the structure of the nucleus.
- Contains: Nuclear envelope(double membrane), nuclear pores, nucleolus (dark spot), DNA / chromatin (wispy stuff),
Name examples of organ systems and their functions.
- Digestive system: digests and processes foods; - Respiratory system: breathing and gas exchange - Circulatory system: pumps and circulates blood.
Describe the structure of chloroplasts (plants and algae)
- Double membrane (chloroplast envelope) - stacks in chloroplast called grana (thylakoid stack) arranged in parallel; maximise surface area being exposed to light - have lamellae joining each grana (granum singular) - stroma (fluid), - have starch grains; food storage - circular DNA & small (70s) ribosomes - chlorophyll absorbs light for photosynthesis
Describe the structure of mitochondria.
- Double membrane; inner membrane folded to form cristae; THIS increases surface area for aerobic respiration. - Matrix containing small 70S ribosomes, small circular DNA and enzymes involved in aerobic respiration (glycolysis)
EQ: Some cells lining the bronchi of the lungs secret large amount of mucus. Mucus contains protein. Name one organelle that you would expect to find in large numbers in a mucus-secreting cell and describe its role in the production of mucus (2 MARKS)
- Golgi apparatus or rough endoplasmic with reticulum or ribosomes or mitchondria or vesicles - Packages / processes proteins or make polypeptide or make ATP (function must be for organelle named).
A photograph was taken using a transmission electron microscope. The structure of the organelles visible in the photograph could not have been seen using an optical (light) microscope. Explain why.
- Has a low resolution - Because wavelength of light is too long / not short enough
Describe the structure of a prokaryotic cell.
- Have no membrane bound organelles!!!!! (No nucleus, gologi, ER, lysosomes, mitochondria, chloroplasts) - Loop of DNA (non linear DNA) (all), no nucleus, DNA free in cytoplasm - Small 70S ribosomes (all); make proteins + rNA - Cell membrane (all) controls what substances goes in and out - Cell wall (all); made of murein (glycoprotein) / peptydolgyican, provides strength and structure - Plasmids (NOT RIBOSOMES); in some, small loop of dNA, can be passed between bacteria, carry useful genes (eg antibiotic resistance) OPTIONAL (not in all): - Capsule; in some, slime layer, adds extra protection - Flagella; in some, rotates to move cell
Describe the advantages of a transmission electron microscope (TEM).
- High resolution (MORE THAN SEM); (electrons have shorter wavelength than light) - allows internal structures of organelles to be seen - High magnification
EQ: Using the labels on the diagram and your own knowledge, give two reasons why this organelle is not a rough endoplasmic reticulum. (3 MARKS)
- It has ribosomes floating inside membrane, in RER ribosomes are attached to membranes not inside - It has DNA, rER doesn't contain DNA - Presence of internal membranes eg thylakoid membrane or grana, rER doesn't have a double membrane
EQ: Figure 1 shows some cell organelles inside the cells of the leaf, but it doesn't show structures such as ribosomes or cell membranes. Use your knowledge of microscopes to explain why this is the case.
- Light microscopes don't have enough resolution AND these organelles are too small - So its not possible to distinguish between two separate points that are close together ** ONLY TALK ABOUT RESOLUTION HERES AS RESOLUTION DETERMINES THE AMOUNT OF DETAIL THAT IS VISIBLE.
EQ: Explain the role of the RER and the Golgi apparatus (5 MARKS).
- Ribosomes attached to RER - Proteins produced by ribosomes, stored and transported within the RER - Proteins folded to tertiary structure and packages these proteins - Golgi modifies / processes protein - Golgi produces lysosomes
In a human, there are over 200 different types of cell clearly distinguishable from each other. What is more, many of these types include a number of different varieties. White blood cells, for example, include lymphocytes and granulocytes. Although different animal cells have many features in common, each type has adaptations. associated with its function in the organism. As an example, most cells contain the same organelles, but the number may differ from one type of cell to another. Muscle cells contain many mitochondria, while enzyme-secreting cells from salivary glands have particularly large amounts of rough endoplasmic reticulum. The number of a particular kind of organelle may change during the life of the cell. An example of this change is provided by cells in the tail of a tadpole. As a tadpole matures into a frog, its tail is gradually absorbed until it disappears completely. Absorption is associated with an increase in the number of lysosomes in the cells of the tail. Use the information in the passage to explain how a tadpole's tail is absorbed as a tadpole changes into a frog.
- Lysosmes produce enzymes - Which hydrolyse cells of tails
Describe the structure and function of the cell wall (plants, algae and fungi).
- Made mainly of cellulose (microfibrils) in plants and algae (or glycoproteins), chitin in fungi - Rigid strong wall surrounding cells - Prevents the cell changing shape and bursting (lysis) - in plants, algae and fungi. - Thin layer middle lamella marks boundary between adjacent cell walls - cellulose is a polysaccharide.
The student decided to produce a biological drawing of a cell. Give two conventions that the student must be sure to follow for their diagram to be classed as a biological drawing.
- Magnification must be included - Structures should be clearly distinguishable - Clear lines (not sketched)
EQ: Human breast milk is produced and secreted by gland cells. These gland cells have adaptations that include many mitochondria and many golgi vesicles. The milk contains a high concentration of protein. Explain the role of these cell adaptations in the production and secretion of breast milk (2 MARKS)
- Many mitochondria for aerobic respiration to release lots of ATP - ATP required in protein synthesis eg translation - Many golgi vesicles for transport (exocytosis) of modified proteins, milk to cell membrane
EQ: The second centrifuge tube was spun at a higher speed then the first to obtain a sample of mitochondria. Suggest why. (1 MARK)
- Mitochondria are less dense then the nucleus
Explain the link between mitochondria and muscle cells; muscle cells contain many mitochondria.
- Mitochondria is site of aerobic respiration - Produces ATP - For contraction
EQ: People with mitochondrial disease have mitochondria that do not function properly. Some people with mitochondrial disease can only exercise for a short time. Explain why a person with mitochondrial disease can only exercise for a short time. (2 MARKS)
- Mitochondria use aerobic respiration to produce ATP - ATP is required for muscles to contract (state function and link to question)
EQ: Name four structures that are present in an epithelial cell from the small intestine but not present in a cholera bacterium (4 MARKS)
- Nucleus - Mitochondrion - Smooth/Rough ER - Lysosome - Golgi - linear; Non-circular DNA - 80s ribosomes
EQ: Figure 1 shows a drawing of part of an animal cell as seen through an electron microscope. Explain why the shapes of the two organelles labelled O in Figure 1 appear different. (2 MARKS)
- Only a cross-section is seen - motocgondria are oriented differently *exam tip: remmeber the organelles can be oriented in any direction in 3D space
EQ: Multicellular organisms contain organs and tissues. Suggest why organs are considered more complex than tissues (3 MARKS)
- Organs are made up of tissues - Organs are made up of many different cell types - Organs can have more than 1 function
Describe the structure and function of the cell-surface membrane.
- Phospholipid bilayer with embedded proteins etc. - Selectively permeable; enables control and entry & exit of passage (movement) of substances in and out of cell - Barrier between internal and external environment of cell
EQ: Describe the procedure that the student would need to follow to prepare a plant cell slide for viewing starch grains under an optical microscope. (3 MARKS)
- Place plant specimen on slide AND use a pipette to place a single drop of stain onto it - Use iodine / potassium iodide stain - Place a cover slip carefully over the top of the sample
Penicillin is an antibiotic. It prevents the formation of bacterial cell walls. As a result, bacterial cells that have been treated with penicillin swell and burst as water enters. Suggest why penicillin has no effect on plant cells.
- Plant cell wall made of cellulose (pencillin doesnt affect cellulose)
What are things prokaryotes have that eukaryotes dont?
- Plasmids present (all) - Slime capsule (some)
EQ: The antibiotic tetracycline binds to ribosomes in bacterial cells. Explain how this causes death of bacterial cells.
- Prevents protein synthesis - So enzymes not produced (enzymes is inhibited)
Prokaryotic cells differ from eukaryotes in having: (COMPARISON QUESTION)
- Prokaryotic cell cytoplasm contains no membrane bound organelles e.g. mitochondria WHEREAS eukaryotic cell contains membrane-bound organelles - Prokaryotic cell has no nucleus / contains FREE-FLOATING DNA in the cytoplasm WHEREAS eukaryotic cell has a nucleus containing DNA - Prokaryotic DNA is shorter, circular and isn't associated with proteins WHEREAS eukaryotic DNA is linear and is associated with proteins (histones) - Prokaryotic cell wall contains the glycoprotein murein and peptidoglycan WHEREAS eukaryotic cell wall is made of cellulose - Prokaryotic cells have smaller 70S ribosomes WHEREAS eukaryotic cells have larger 80S ribosomes - Prokaryotic cells may have a capsule and/or one or more flagella
Describe the structure and function of the rough endoplasmic reticulum. (RER)
- Ribosomes attached by a system of fluid filled membranes, usually attached to nucleus - proteins produced by ribosomes, stored and transported within RER - Translation; Large surface area to modify and fold proteins (polypeptides) to a tertiary structure - Packages proteins to vesicles, transport to the Golgi apparatus etc.
Describe the structure and function of the smooth endoplasmic reticulum. (SER)
- Similar to rough endoplasmic reticulum but without ribosomes - system of membranes - Synthesises, processes and transports lipids & carbohydrates
EQ: Explain why there are lots of mitochondria in a cell from the pancreas.
- Site of aerobic respiration - Release ATP - For active transport (explain: state function and link to question)
Name the order in which specialised cells are organised into complex multicellular organisms:
- Specialised cell - Tissue - Organ - Organ system - Organism
EQ: A student wanted to view starch grains under an optical microscope, and their teacher told them to use a stain in order to do this. State why the student would need to use a stain to view starch grains. (1 MARK)
- Stain allow colourless objects to be seen clearly
EQ: A student used an optical microscope to view a specimen. They wanted to work out the actual size of the specimen, and decided to use a stage micrometer together with the ruler visible inside the eyepiece of the microscope (known as the eyepiece graticule). State why a stage micrometer is needed as well as the eyepiece graticule. (2 MARKS)
- The size of the units of the eyepiece graticule change depending on the magnification being used - The micrometer can be used to calibrate the graticule.
EQ: Explain why the homogenate was filtered before spinning at low speed in the centrifuge. (2 MARKS)
- To remove / filter any cell debris or unwanted unbroken whole cells (and / or connective tissue) - Which would contaminate the sediment and interfere with the results.
Describe the structure and function of lysosomes.
- Type of Golgi vesicle, membrane bound organelle sac containing lysozymes - digestive / hydrolytic enzymes - Release of lysozymes to break down / hydrolyse pathogens or worn-out cell components
Describe the principles of how transmission electron microscopes (TEM) uses electrons to generate an image.
- Use electrons to form a 2D image by - Electromagnets focus beam of electrons THROUGH thin specimen, transmitted, denser parts absorb more electrons = darker appearance, (so less dense = less absorbed = light appearance) - Electrons shorter wavelength (so higher resolution 0.2 nm) - High magnification x1500000 (or 500,00x)
Describe scanning electron microscopes (SEM).
- Use electrons to form a 3D image - Beams of electrons scan surface, knocking off electrons from the specimen, which are gathered in a cathode ray tube to form an image - Electrons have shorter wavelength (so higher resolution 0.2 nm) - High magnification x1500000
Describe the limitations of a scanning electron microscope (SEM).
- Vacuum; cant see living organisms - Lower resolution than TEM - Can't see internal structures
EQ: Structures V to Z are organelles within a plant cell. V - Nucleus W - Chloroplast X - Golgi Apparatus Y - Mitochondrion Z - Cell Wall Complete the table by identifying the correct letter next to each statemenr (4 MARKS)
- W - Z - V - X
EQ: Mammals feed their young with milk that is synthesized and expressed by mammary gland cells. These gland cells have evolved to contain large numbers of mitochondria and Golgi apparatus. The milk contains a high concentration of protein to feed an infant's growth. Explain how these adaptations could aid the synthesis and expression of milk. (2 MARKS)
- a large number of mitochondria; produces atp for movement and exocytosis of vesicles - a large number of golgi appartus; transport protein / glycoprotein / milk to the cell membrane
EQ: Describe how you could make a temporary mount of a piece of tissue to observe when using a light microscope. (4 MARKS)
- add drop of water to glass slide - obtain thin section of tissue and place on slide - stain with iodine in potassium iodide - lower cover slip using mounted needle
Give an advantage of using SEM rather than TEM.
- can have 3D images - sections dont have to be prepared - can be used on thicker specimens
EQ: The scientists carried out a further investigation. They treated the liquid from strain A with a protein-digesting enzyme before adding it to a culture of human cells. No cell damage was recorded. Suggest why there was no damage to the cells
- enzyme is broken down - no toxin - so toxin is protein
Explain the link between rough endoplasmic reticulum and enzyme-secreting cells from salivary glands:
- enzymes are proteins - proteins synthesised on ribosomes
Describe the advantages of a scanning electron microscope (SEM).
- forms 3D image - High magnification, High resolution; (shorter wavelength of electron than light) - Used on thick specimens (dont need thin section)
EQ: Describe how a sample of chloroplasts could be obtained from leaf tissue using cell fractionation techniques. You will not gain any marks for including information about any solutions in your answer (3 Marks)
- homogenise the cells in solution - centrifuge - at different increasing speeds until chloroplast fraction obtained
EQ: Figure 1 shows a diagram of an organism called Chlamydomonas that lives in freshwater. Use the figure to explain three adaptations of Chlamydomonas that enables this organism to maintain a high rate of photosynthesis. (3 MARKS)
- light sensitive eyespot - flagellum enables movement towards light - large surface area of chloroplast to absorb light OR chloroplast contains large amount of chlorophyll to absorb light for photosynthesis (for the third mark you must explain how the size of the chloroplast or amount of chlorophyll contributes towards a high rate of photosynthesis.)
EQ: Figure 1 shows the structure of the organism Chlamydomonas. Name three structures shown in Figure 1 that are present in eukaryotic cells but are not present in prokaryotic cells. (3 MARKS)
- light-sensitive eye spot - nucleus - starch granule
Describe the structure and function of ribosomes.
- made of proteins + RNA - has 1 larger and 1 smaller subunit - 80S- eukaryotic cells, 70S- prokaryotic cells, mitochondria, chloroplasts - Float in cytoplasm or bound to rough endoplasmic reticulum. Not membrane bound. - site of protein synthesis, specifically translation
Name the eukaryotic structures that cannot be identified using an optical microscope.
- mitochondrion - ribosome - endoplasmic reticulum - lysosome - cell-surface membrane (don't say chloroplasts to be safe because they could be talking about an animal cell)
From a mitochondrion and chloroplast, which organelle has the diffusion of oxygen into the organelle and which organelle has the diffusion of carbon dioxide into the organelle?
- mitochondrion: diffusion of oxygen into organelle (for aerobic respiration) - chloroplast: diffusion of carbon dioxide into organelle (for photosynthesis)
EQ: A stomach ulcer is caused by damage to the cells of the stomach lining. People with stomach ulcers often have the bacterium Helicobacter pylori in their stomachs. A group of scientists was interested in trying to determine how infection by H. pylori results in the formation of stomach ulcers. The scientists grew different strains of H. pylori in liquid culture. The table below shows the substances released by each of these strains. The scientists centrifuged the cultures of each strain to obtain cell-free liquids. They added each liquid to a culture of human cells. They then recorded the amount of damage to the human cells. Their results are shown below. The error bars show ± 1 standard deviation. What do these data suggest about the damage caused to human cells by the toxin and by the enzyme that neutralises acid? Explain your answer. (3 MARKS)
- more cell damage when both present - some cell damage when either there on their own - standard deviation doesn't overlap A and B so difference is real - standard deviations do overlap B and C so no real difference
Describe the structure and function of the golgi apparatus:
- not surrounded by two membranes. - group of 3 or more fluid-filled membrane-bound sacs with vesicles at edge - Receives protein from rER - modifies/processes/ protein, e.g. add carbohydrates (form glycoproteins) and lipids - Repackages into golgi vesicles e.g. for transport to cell surface membrane for exocytosis - Also makes lysosomes
Give the two types of molecule from which a ribosome is made.
- one of RNA (ribonucleic acids) - one of proteins / polypeptides
EQ: Suggest what kind of organism Chlamydomonas is, based on the information shown in Figure 1. Give reasons for your suggestion (2 MARKS)
- photosynthetic organism; as it contains a chloroplast (and stored starch) - it is an alga / eukaryote; as it contains a primitive sight organ
EQ: Large numbers of mitochondrion are found in the small intestine epithelial cells. Explain why these cells are adapted in this way. (3 MARKS)
- provide energy by producing ATP - high aerobic respiration rate for active transport - absorption of digested food EXPLANATION: - saying create(s) energy wouldn't be accepted. energy cannot be created it can only be transferred - saying for respiration for the second mark isn't enough, you must link the large numbers of mitochondria with the high respiration rate of these cells - it is important to state why the small intestine epithelial cells would need to produce more atp, it is because they do a lot of active transport - for the third marking point, only monosaccharides, amino acids or dipeptides would be accepted as a named product.
Name a detail that would make it visible that a transmission electron microscope was used.
- smaller organelles become visible eg mitochondrion
Describe the limitations of a transmission electron microscope (TEM).
- specimens must be dead, in a Vacuum; cant see living cells - Complex 'staining' preparation process is required (image only black & white; no coloured image produced) - Image may contain artefacts from preparation process - 2D image - Only used on thin specimens
Describe optical microscopes.
- uses light to form 2D image - Visible light longer wavelength so lower resolution 200nm - low magnification of x1500
What is the size of prokaryotic cells?
0.1 to 5 micrometers
What is one mm in nanometers?
1,000,000
Label this fungal cell:
1. Cytoplasm 2. Rough endoplasmic reticulum 3. Smooth endoplasmic reticulum 4. Golgi apparatus 5. Vacoule 6. Cell wall (chitin) 7. Cell membrane 8. Nuclear envelope 9. Nucleus 10. Nucleolus 11. Lysosome 12. Mitochondria 13. Ribosome
EQ: Describe and explain how centrifuging the culture allowed the scientists to obtain a cell-free liquid. (3 MARKS)
1. Large / dense cells; 2. Form pellet / move to the bottom of the tube (when centrifuged) 3. Liquid / supernatant can be removed.
Describe the principles of cell fractionation and ultracentrifugation as used to separate cell components:
1. Place in a cold, isotonic, buffered solution - Cold reduces/prevents enzyme activity so organelles arent broken down (digested) - Isotonic prevent damage to cells by preventing osmosis so water doesn't move in/out of organelles dont burst / shrivel - Buffered regulates pH so its constant so enzymes & proteins dont denature (damage) 2. Homogenise tissue using blender - Disrupts the cell membrane / break open the cell - Release contents / organelles 3. Filter homogenate through gauze - Remove cell debris and large unbroken whole cells (or connective tissue) 4. Ultracentrifugation - Centrifuge (spin) homogenate in a tube at a low (slow) speed - Densest organelle compressed into pellet at the bottom, remove this and re-spin remaining liquid (supernatant) at a higher speed to get second pellet of next heaviest organelle - Repeated at higher and higher speeds until organelles separated out, each time pellet is made of less dense organelles - Separated in order of density: first pellet nuclei → second pellet chloroplasts → mitochondria → lysosomes → endoplasmic reticulum → ribosomes NCMLER = Never compare my lousy evil relationships
Label this animal cell:
1. Rough endoplasmic reticulum 2. Smooth endoplasmic reticulum 3. Cytoplasm 4. Golgi apparatus 5. Cell-surface membrane 6. Nuclear envelope 7. Nucleus 8. Nucleolus 9. Mitochondria 10. Ribosome 11. Lysosome
Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells. (6 MARKS)
1. TEM use electrons & focuses using magnets and optical use light and focuses glass lenses 2. TEM has higher resolution so smaller organelles can be observed unlike in optical 3. TEM view only dead specimens whereas optical can view live specimens 4. TEM is black&white with no colour and optical has colour 5. TEM requires thinner specimens than optical 7. TEM requires more complex preparation
EQ: Figure 1 shows a cross section of a leaf taken using an optical microscope with a magnification of x250. Use the information provided to calculate the actual length of a palisade cell, as marked by line A on figure 1. Give your answer in micrometers.
Actual size = image size / magnification - 20,000 / 250 = 80 micrometers
Describe how proteins are produced, synthesised, modified and transported out of the cell. (5 MARKS)
SEVEN STEPS: 1. Nucleus: contains the gene for the protein, site of transcription (DNA —> mRNA) 2. Protein synthesis translation ( mRNA) takes place on the ribosomes often on the rER, making the primary sequence for proteins. rER folds proteins to form 3d tertiary structure. 3. Protein is packaged into rER vesicles and transported to golgi apparatus / body in a vesicle. 4. Golgi apparatus processes and modifies the protein eg adds a carbohydrate (or lipid) —> glycogen protein 5. Protein is repackaged into a golgi vesicle for transport 6. Vesicle is transported to cell-surface membrane 7. Exocytosis; vesicle fuses with the membrane
EQ: Bacteriophages are viruses that kill bacteria. Researchers investigated the use of bacteriophages to alleviate the symptoms of bacterial lung infections. They inoculated the lungs of rats with a pathogenic bacterium. The rats were then divided into two groups, J and K: - The rats in group J were untreated - the rats in group K were given bacteriophage treatment by means of an aerosol spray that they inhaled. After 5 days, the researchers killed the rats and excised their lungs. The lungs were washed out with a set volume of fluid. The researchers used a technique to count the number of live bacteria in the fluid. Figure 1 shows the researchers' results. The mean and the range of the data are shown for each group. In some cases, the researchers needed to carry out a serial dilution of the sample before performing a count of the bacteria. Use data from the table to account for the researcher's choices to perform serial dilutions in some cases but not for others. (2 MARKS)
Serial dilution was chosen in some cases because: - The log scale captures a wide range of bacteria numbers - Some samples will contain too many bacteria to count (so should be diluted) whereas some samples are countable undiluted (You need to understand the logarithmic scales to achieve full marks for this question! The log scale gives numbers of bacteria per cm3 that differ in orders of magnitude)
EQ: Bacteriophages are viruses that kill bacteria. Researchers investigated the use of bacteriophages to alleviate the symptoms of bacterial lung infections. They inoculated the lungs of rats with a pathogenic bacterium. The rats were then divided into two groups, J and K: - The rats in group J were untreated - the rats in group K were given bacteriophage treatment by means of an aerosol spray that they inhaled. After 5 days, the researchers killed the rats and excised their lungs. The lungs were washed out with a set volume of fluid. The researchers used a technique to count the number of live bacteria in the fluid. Figure 1 shows the researchers' results. The mean and the range of the data are shown for each group. Using only the graph given, analyse the effectiveness of the bacteriophage in treating the lung infection in rats. Do not consider statistical analyses in your answer (3 MARKS)
The bacteriophage... - Decreased the count of bacteria in the lungs of rats - In all cases because the ranges dont overlap - There is a wide range of effects; it doesnt bring bacteria down to 0 in any rats
EQ: Scientists investigated the effect of an exercise programme on the number and area of the inner mitochondrial membranes in the skeletal muscle. They took samples of muscle from a large number of volunteers before and after the exercise programme. From each sample, they cut thin sections and used these to determine the mean number of mitochondria per micrometers2 and the mean area of inner mitochondrial membranes. The results are shown in Table 1. Using the data from Table 1, suggest the effect of the exercise programme on the mitochondria. (2 MARKS)
The effect of exercise on mitochondria: - training made no difference to the number of mitochondria per micrometer2 - training led to significant increase in the area (of the inner mitochondrial membrane)
EQ: Bacteriophages are viruses that kill bacteria. Researchers investigated the use of bacteriophages to alleviate the symptoms of bacterial lung infections. They inoculated the lungs of rats with a pathogenic bacterium. The rats were then divided into two groups, J and K: - The rats in group J were untreated - the rats in group K were given bacteriophage treatment by means of an aerosol spray that they inhaled. After 5 days, the researchers killed the rats and excised their lungs. The lungs were washed out with a set volume of fluid. The researchers used a technique to count the number of live bacteria in the fluid. Figure 1 shows the researchers' result. The mean and the range of the data are shown for each group. Suggest the scientists' null hypothesis and experimental hypothesis for this investigation. (2 MARKS)
The null hypothesis: - The bacteriophage has no effect on the number of bacteria The experimental hypothesis: - The bacteriophage has an effect on the number of bacteria
EQ: An outbreak of cholera occured in London in 1849. Figure 2 shows the relationship between the number of deaths from cholera and the height at which people lived above sea level. Describe the results shown in Figure 2.
The relationship between the number of deaths from cholera and the height at which people lived above sea level...... - There is a sharp decline in deaths after the height reaches 30 feet - As the height above sea level increases, the number of deaths decreases (inversely proportional relationship / negative correlation ) (MUST DESCRIBE TREND NOT JUST INDIVIDUAL POINTS ON GRAPH).
What is the process in which cells become specialised?
differentiation
Describe algae:
eukaryotes, single celled but other than that they are the same as plant cells
What is the singular of grana?
granum
