Organelles & Compartmentalisation

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शिक्षकों के लिए: Organelles & Compartmentalisation (Biology, SL) के लिए इस्तेमाल के लिए तैयार लेसन स्लाइड्स, रिवीज़न नोट्स — इन्हें अपने लेसन में इस्तेमाल करें, या टॉपिक को एक इंटरैक्टिव क्लास एक्टिविटी की तरह चलाएं जिसे आपके शिक्षार्थी लाइव गेम की तरह खेलें।

लेसन नोट्स

Eukaryotic Cell Compartmentalisation

Eukaryotic cells have a more complex ultrastructure than prokaryotic cells.
The cytoplasm is divided into membrane-bound compartments called organelles.
Organelles are bound by either a single or double membrane.
Structures without a membrane — cell wall, cytoskeleton and cytoplasm — are not considered organelles.
Compartmentalised organelles include the nucleus, vesicles, ribosomes and the plasma membrane.

Advantages of Compartmentalisation

Enzymes and substrates can be localised, so they are available at higher concentrations.
Damaging substances can be kept separate — e.g. digestive enzymes are stored in lysosomes so they do not digest the cell.
Optimal conditions can be maintained for certain processes, e.g. optimal pH for digestive enzymes.
The number and location of organelles can be altered depending on the cell's requirements.

Organelle Adaptations

In complex cells, organelles can become specialised for specific functions.
Specialised organelles have specific adaptations that help them carry out their functions.
The structure of an organelle is adapted to its function — this is why each organelle looks very different.
Separation by a membrane (sometimes double) allows an organelle to carry out its own chemical reactions without interference from the rest of the cell.

Structure of a mitochondrion

Cell Fractionation

Progress in science often follows the development of new techniques.
Study of individual organelles became possible after the invention of ultracentrifuges and the development of cell fractionation methods.
Cell fractionation separates out each compartment so it can be studied individually; a pure sample containing only the specific organelle is needed.
The process involves breaking up a suitable tissue sample and then centrifuging the mixture at different speeds.

Stages of Cell Fractionation

Homogenisation — the cell sample is broken up using a homogeniser (a blender-like machine).
Filtration — the homogenate is filtered through a gauze.
Ultracentrifugation — the filtrate is placed into a tube and spun in a centrifuge.
A centrifuge separates materials by spinning; the speed can be altered to separate different components based on their molecular weight.
Before the ultracentrifuge was invented, research into separate organelles was limited.

Separating the Nucleus and Cytoplasm

The nucleus is a key organelle that distinguishes eukaryotic cells from prokaryotic cells.
It allows many cell processes to take place more efficiently than in prokaryotes.
Gene transcription and translation occur in both eukaryotes and prokaryotes.
In prokaryotes these processes take place simultaneously, allowing rapid responses to environmental stimuli.
In eukaryotes they occur separately due to the compartmentalisation of the nucleus.
During transcription, mRNA is formed using a template strand of DNA; the mRNA needs modification before it can be used for translation.
Modification takes place in isolation within the nucleus before the mRNA contacts a ribosome (where translation occurs), unlike in prokaryotes where mRNA immediately meets a ribosome.
This reduces the chance of errors in the mRNA code and therefore in the resulting protein after translation.

The nucleus

Compartmentalisation in the Cytoplasm

The cytoplasm is not considered an organelle, but its separation from organelles via their membranes is an advantage.
Organisation into discrete membrane-bound organelles allows separation of incompatible biochemical processes.
This ensures pathways requiring specific enzymes or metabolites run smoothly without interference from other cell structures or chemicals.
Conflicting reactions can coexist within one organelle by being localised — e.g. in plant cells, nitrogenase (used for nitrogen fixation) is sensitive to oxygen and is positioned in an anaerobic part of the cytoplasm away from aerobic reactions.
Lysosomes contain lytic enzymes that could be harmful to the cell if not contained by the lysosome membrane.
During endocytosis, a phagocytic vacuole forms around potentially toxic and harmful substances (such as bacteria), keeping them separate from the cytoplasm until a lysosome can safely digest the material.

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साइन अप करें — फ्री लॉग इन

प्रैक्टिस सवाल

फ्री प्रीव्यू — 60 में से 8 सवाल। सभी देखने के लिए साइन अप करें।

1.Which of the following is true of ribosomes?
Easy
- AProteins for transport are synthesised by free ribosomes.
- BRibosomes consist of a large and a small subunit composed of protein and transfer RNA (tRNA).
- CRibosomes exist in the cells of all living organisms.
- DRibosomes on the rough endoplasmic reticulum synthesise proteins for retention within the cell.
2.The chloroplast is adapted for photosynthesis. Which of the following is not an adaptation of the chloroplast for photosynthesis?
Medium
- AA large surface area of thylakoid membranes with photosystems.
- BA large volume of fluid inside thylakoids.
- CCompartmentalisation of enzymes and substrates of the Calvin cycle in the stroma.
- DChloroplast DNA that contains genes which code for some of the proteins and enzymes used in photosynthesis.
3.Which of the following is not considered an organelle because it lacks a membrane?
Easy
- ANucleus
- BMitochondrion
- CCell wall
- DLysosome
4.The cytoplasm is divided up into membrane-bound compartments called organelles in eukaryotic cells.
Easy
True or false?
5.Which of the following are advantages of compartmentalisation in eukaryotic cells? (select all that apply)
Medium
- AEnzymes and substrates can be localised at higher concentrations.
- BDamaging substances such as digestive enzymes can be kept separated from the rest of the cell.
- CAll chemical reactions in the cell occur simultaneously in the cytoplasm.
- DOptimal conditions such as pH can be maintained for specific processes.
- EThe number and location of organelles can be altered depending on the cell's requirements.
6.Match each organelle or structure with its correct description.
Medium
- Nucleus
- Lysosome
- Ribosome
- Chloroplast
- Contains digestive enzymes kept separate from the cytoplasm
- Site of protein synthesis; not membrane-bound
- Double-membrane organelle containing thylakoids and stroma
- Double-membrane organelle containing DNA and site of transcription
7.Place the steps of cell fractionation in the correct order.
Medium
- Homogenisation of tissue
- Filtration through gauze
- Ultracentrifugation at increasing speeds
- Collection of organelles by size
8.Match each structure to whether it is bound by a single membrane, a double membrane, or no membrane.
Medium
- Nucleus
- Lysosome
- Ribosome
- Cell wall
- Double membrane
- Single membrane
- No membrane

और सवाल

9.Which of the following structures are not considered organelles because they lack a membrane? (select all that apply)
Medium
- ACytoskeleton
- BCytoplasm
- CCell wall
- DNucleus
- EVesicle
10.Place the stages of cell fractionation in the correct sequence.
Medium
- Ultracentrifugation
- Homogenisation
- Filtration
11.During ultracentrifugation, in which order are organelles collected from the filtrate as the spinning speed increases?
Medium
- ANuclei, then mitochondria, then ribosomes
- BRibosomes, then mitochondria, then nuclei
- CMitochondria, then nuclei, then ribosomes
- DNuclei, then ribosomes, then mitochondria
12.In prokaryotes, transcription and translation occur simultaneously, whereas in eukaryotes compartmentalisation separates these processes.
Easy
True or false?
13.In plant cells, the enzyme nitrogenase is sensitive to oxygen. How does compartmentalisation help it function?
Medium
- AIt is positioned in an anaerobic part of the cytoplasm away from aerobic reactions
- BIt is stored inside the lysosome with digestive enzymes
- CIt is enclosed within the double membrane of the nucleus
- DIt is moved into the thylakoid space of the chloroplast
14.Which step breaks up the cells using a blender-like machine?
Medium
- AHomogenisation
- BFiltration
- CUltracentrifugation
- DCentrifugation
15.Filtration removes large, unbroken pieces of tissue from the homogenate.
Easy
True or false?
16.A scientist wants to isolate intact chloroplasts from spinach leaves. Which of the following best explains why the tissue is homogenised in a cold, isotonic buffer solution?
Medium
- ATo keep the organelles at an optimal temperature for enzyme activity during the separation process
- BTo prevent the organelles from shrinking or bursting and to reduce enzyme activity that could digest them
- CTo increase the density of the organelles so that they sediment more quickly during ultracentrifugation
- DTo dissolve the membranes surrounding the organelles so that their contents can be released
17.A student centrifuges a liver homogenate. After the first spin at 1000 × g, a pellet forms. The supernatant is then spun at 20,000 × g, producing a second pellet. Which organelle is most likely to be the main component of the second pellet?
Medium
- ANuclei
- BMitochondria
- CRibosomes
- DGolgi apparatus
18.A cell biologist is studying a rare metabolic disorder in which lysosomes are leaky. Which of the following cellular processes would be directly affected? (select all that apply)
Medium
- ADigestion of material taken in by phagocytosis
- BSynthesis of proteins on the rough endoplasmic reticulum
- CBreakdown of worn-out organelles
- DPackaging of proteins into vesicles
- EMaintenance of an acidic environment for hydrolytic enzymes
19.In a plant root nodule, the enzyme nitrogenase is irreversibly damaged by oxygen. Which feature of cell compartmentalisation best explains how nitrogenase can function in these cells?
Hard
- ANitrogenase is enclosed in a double-membrane organelle that excludes all oxygen
- BNitrogenase is located in an anaerobic region of the cytoplasm separated from aerobic reactions
- CNitrogenase is packaged into lysosomes where oxygen is actively removed
- DNitrogenase is bound to the outer surface of the plasma membrane where oxygen levels are lowest
20.A researcher uses a centrifuge that spins at 12,000 revolutions per minute. How many revolutions will it complete in 2.5 minutes?
Medium
- A4,800
- B24,000
- C30,000
- D48,000
21.During cell fractionation, the order in which organelles are collected from the filtrate depends on their size and density, with the largest and densest organelles sedimenting first.
Easy
True or false?
22.Match each stage of cell fractionation with its correct description.
Medium
- Homogenisation
- Filtration
- Ultracentrifugation
- The cell sample is broken up using a blender-like machine
- The homogenate is passed through a gauze to remove large pieces of tissue
- The filtrate is spun at different speeds to separate organelles by size and density
23.Place the following steps of cell fractionation in the correct order.
Medium
- Homogenise the tissue sample
- Filter the homogenate through gauze
- Centrifuge the filtrate at a low speed
- Centrifuge the supernatant at a higher speed
24.Based on the table, which organelle would be collected first during ultracentrifugation?
Medium
- ARibosomes
- BMitochondria
- CNuclei
- DVesicles
25.The student wants to obtain a pure sample of mitochondria. Which step should be taken after the first low-speed centrifugation?
Hard
- ADiscard the pellet and centrifuge the supernatant at a higher speed
- BDiscard the supernatant and keep the pellet for analysis
- CFilter the pellet again through gauze
- DHomogenise the pellet a second time
26.A student homogenises liver tissue in a cold, isotonic buffer. Why is the buffer kept cold?
Medium
- ATo reduce the activity of enzymes that would digest the organelles
- BTo increase the rate at which the organelles sediment
- CTo make the homogenate denser so it filters faster
- DTo break open the cells more effectively
27.During cell fractionation, why is the homogenate filtered through gauze before ultracentrifugation?
Medium
- ATo remove large, unbroken pieces of tissue and cell debris
- BTo separate organelles according to their density
- CTo break open the remaining intact cells
- DTo keep the sample at a constant temperature
28.A student spins a homogenate first at 1,000 × g and then at 20,000 × g. Which organelle is most likely to be in the pellet after the second spin?
Medium
- AMitochondria
- BNuclei
- CRibosomes
- DIntact cells
29.Which of the following would help a student obtain a pure sample of a single organelle type? (select all that apply)
Medium
- AUsing a cold, isotonic buffer during homogenisation
- BCentrifuging the homogenate at increasing speeds in steps
- CFiltering the homogenate through gauze before centrifuging
- DShaking the homogenate vigorously between spins
- EKeeping the centrifuge at a warm temperature
30.In cell fractionation, the largest and densest organelles are collected in the pellet after the lowest-speed centrifugation.
Easy
True or false?
31.Match each cell fractionation stage with its correct description.
Medium
- Homogenisation
- Filtration
- Ultracentrifugation
- Breaking up the cell sample with a blender-like machine
- Passing the homogenate through a gauze
- Spinning the filtrate at different speeds in a centrifuge
32.Why is it advantageous that digestive enzymes are kept inside lysosomes rather than free in the cytoplasm?
Medium
- AThe lysosome membrane keeps the enzymes separate so they do not digest the cell
- BThe lysosome membrane allows the enzymes to work at a higher temperature
- CThe lysosome membrane increases the concentration of oxygen around the enzymes
- DThe lysosome membrane stops the enzymes from being synthesised
33.The optimum pH for these lysosomal enzymes is about 5. Which statement best explains how compartmentalisation allows this optimum to be maintained?
Hard
- AThe lysosome membrane maintains a different pH inside the lysosome from the cytoplasm
- BThe cytoplasm is acidic, so the enzymes work at pH 5 there
- CThe enzymes change their optimum pH to match the cytoplasm
- DThe lysosome has no membrane, so pH is the same inside and outside
34.Which of the following structures is not considered an organelle because it lacks a membrane?
Easy
- ACytoskeleton
- BNucleus
- CLysosome
- DMitochondrion
35.The cell wall is not considered an organelle because it is not bound by a membrane.
Easy
True or false?
36.Which of the following are compartmentalised organelles of a eukaryotic cell? (select all that apply)
Medium
- ANucleus
- BVesicle
- CCytoplasm
- DRibosome
- EPlasma membrane
37.Which of the following is an advantage of compartmentalisation in a eukaryotic cell?
Easy
- AEnzymes and substrates can be localised at higher concentrations.
- BAll chemical reactions in the cell occur in a single compartment.
- CDamaging substances are mixed freely with the cytoplasm.
- DThe cell no longer requires a plasma membrane.
38.A plant cell carries out nitrogen fixation using the enzyme nitrogenase, which is sensitive to oxygen. Where is nitrogenase positioned to allow it to function?
Medium
- AIn an anaerobic part of the cytoplasm, away from aerobic reactions
- BInside the mitochondrion, where oxygen is used
- CIn the nucleus, alongside the DNA
- DIn the thylakoid space of the chloroplast
39.Match each term with its correct definition.
Easy
- Compartmentalisation
- Organelle
- Homogenisation
- The division of the cytoplasm into membrane-bound compartments
- A membrane-bound structure within a cell that carries out a specific function
- The breaking up of a cell sample using a blender-like machine
40.Which statement best explains why the separation of the nucleus from the cytoplasm reduces errors in the resulting protein?
Medium
- AmRNA can be modified in isolation within the nucleus before it reaches a ribosome.
- BDNA is translated directly into protein inside the nucleus.
- CRibosomes enter the nucleus to carry out translation there.
- DTranscription and translation occur simultaneously, allowing rapid correction.
41.Complete the sentence about cell fractionation.
Easy
The cell sample is broken up using a ____ in a process called homogenisation, and the mixture is then spun at different speeds in a(n) ____.
42.A centrifuge is set to spin at 15000 revolutions per minute. How many revolutions will it complete in 2 minutes?
Medium
43.Complete the sentence about a benefit of compartmentalisation.
Medium
Digestive enzymes are stored inside ____ so that they do not digest the cell.
44.Name the machine used to separate cellular organelles by spinning at different speeds.
Medium
45.A centrifuge spins at 12,000 revolutions per minute. How many revolutions does it complete in 3 minutes?
Medium
46.A centrifuge spins at 8,000 revolutions per minute. How many revolutions does it complete in 4 minutes?
Medium
47.Name the machine that separates cellular organelles by spinning at different speeds.
Easy
48.Complete the sentence about compartmentalisation in eukaryotic cells.
Easy
The cytoplasm of eukaryotic cells is divided up into membrane-bound compartments called ____.
49.Complete the sentence about the advantage of compartmentalisation.
Medium
Compartmentalisation allows enzymes and substrates to be localised, so they are available at higher ____.
50.Complete the sentence about the first stage of cell fractionation.
Medium
During cell fractionation, the cell sample is broken up by a blender-like machine in a stage called ____.
51.Complete the sentence about the machine used in cell fractionation.
Easy
The filtrate is placed into a tube and spun in a machine called a ____, which separates materials by spinning.
52.Name the stage of cell fractionation in which the homogenate is passed through a gauze.
Medium
53.Define compartmentalisation.
Medium
54.In addition to the mitochondria, identify two other compartmentalised structures with double membranes characteristic of a eukaryotic cell.
Medium
55.The ability to isolate organelles led to progress in the understanding of organelle structures and function. (i) Describe the technique used to separate cellular organelles by size. (ii) Explain the order in which the organelles would be collected using this method.
Hard
56.Explain why the separation of the nucleus from the cytoplasm is an advantage in eukaryotic cells.
Hard
57.Explain how the separation of the nucleus from the cytoplasm in eukaryotic cells reduces the chance of errors in the resulting protein.
Hard
58.A centrifuge is set to spin at 15000 revolutions per minute. How many revolutions will it complete in 2 minutes?
Medium
- A30000 revolutions
- B36000 revolutions
- C27000 revolutions
- D33000 revolutions
59.A centrifuge spins at 12,000 revolutions per minute. How many revolutions does it complete in 3 minutes?
Medium
- A43200 revolutions
- B32400 revolutions
- C39600 revolutions
- D36000 revolutions
60.A centrifuge spins at 8,000 revolutions per minute. How many revolutions does it complete in 4 minutes?
Medium
- A32000 revolutions
- B28800 revolutions
- C35200 revolutions
- D38400 revolutions

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