Cell: The Unit of Life ISC Class 11: Structure and Function of Organelles

What Cell: The Unit of Life is about

Weightage: Cell: The Unit of Life belongs to the unit Cell: Structure and Function, which CISCE weights at 15 of the 70 marks in the ISC Class XI Biology Paper I (Theory). Class XI is examined by the school, so your school sets the paper within this weightage.Source: CISCE ISC Biology syllabus, examination year 2028, Class XI unit weightage

Key concepts

Cell theory, history, size and shape

History: Robert Hooke (1665) saw box-like compartments in thin slices of cork and called them cells (they were dead cell walls). Antonie van Leeuwenhoek first saw and described living cells (bacteria, protists) with his own lenses. Robert Brown (1831) discovered the nucleus. Matthias Schleiden (1838), a botanist, concluded that plants are made of cells; Theodor Schwann (1839), a zoologist, reached the same conclusion for animals and noted the cell wall as a feature of plant cells; together they proposed the cell theory. Rudolf Virchow (1855) added that new cells arise only from pre-existing cells (*omnis cellula e cellula*). Modern cell theory: (1) all living organisms are made of cells and cell products; (2) the cell is the basic unit of structure and function; (3) all cells arise from pre-existing cells. Size: *Mycoplasma*, the smallest known cells, are about 0.3 µm; bacteria are about 3–5 µm; a human red blood cell is about 7 µm across; the egg of an ostrich is the largest single cell; nerve cells are among the longest. Shape relates to function: disc-shaped RBCs for gas transport, long branched neurons for conduction, columnar cells for absorption, irregular amoeboid white cells for engulfing microbes.

Worked example

Why did Hooke's observation not prove the cell theory by itself?

Try it first, then show the solutionSolution

1. Hooke saw only empty walls of dead cork cells, not living contents
2. The ideas that all organisms are cellular and that cells come from cells needed Schleiden, Schwann and Virchow

Answer: He named cells but did not show that they are the living unit of all organisms or that they arise from existing cells

Plasma membrane: fluid mosaic model and transport

The fluid mosaic model (Singer and Nicolson, 1972) describes the membrane as a lipid bilayer of phospholipids, with polar (hydrophilic) heads facing the watery outside and inside and non-polar (hydrophobic) tails facing each other, with cholesterol among them. Proteins are scattered like a mosaic: integral proteins are buried partly or fully in the bilayer; peripheral proteins sit on the surface. Carbohydrates attached to lipids and proteins (glycolipids, glycoproteins) face outwards. The bilayer is quasi-fluid, so proteins and lipids can move sideways; this fluidity is needed for growth, cell junctions, secretion, endocytosis and division. Passive transport needs no energy and moves substances down a concentration gradient: simple diffusion (O₂, CO₂, small non-polar molecules) and osmosis (movement of water across a selectively permeable membrane). Facilitated diffusion: polar molecules and ions that cannot cross the lipid bilayer move down their gradient through specific carrier or channel proteins, without ATP. Carriers are of three kinds: a uniport moves one substance in one direction (glucose into red blood cells by a glucose transporter); a symport moves two substances in the same direction (Na⁺ and glucose entering intestinal cells together, glucose riding on the Na⁺ gradient); an antiport moves two substances in opposite directions (Cl⁻ in and HCO₃⁻ out of red blood cells, the chloride shift). Active transport moves substances against a gradient using ATP, e.g. the Na⁺/K⁺ pump, which expels 3 Na⁺ and takes in 2 K⁺ per ATP (itself an antiport).

Worked example

Glucose enters a red blood cell by moving down its concentration gradient through a carrier, without ATP. Name the process and type of carrier.

Try it first, then show the solutionSolution

1. Movement down a gradient through a protein carrier with no ATP is facilitated diffusion
2. Only one substance moves, in one direction: uniport

Answer: Facilitated diffusion through a uniport

Cell wall and cell envelope

The cell wall is a non-living, rigid outer layer outside the plasma membrane of plant cells, fungi and bacteria; it gives shape, protects against mechanical damage and infection, helps cell-to-cell interaction and prevents bursting in dilute solutions. Plant wall: cellulose, hemicellulose, pectins and proteins. Fungal wall: chitin. Algal wall: cellulose, galactans, mannans and minerals such as calcium carbonate. Young plant cells have a thin, elastic primary wall that allows growth; later a thicker secondary wall is laid down inside it. Neighbouring cells are cemented by the middle lamella, mainly calcium pectate. The wall and middle lamella are crossed by plasmodesmata, fine cytoplasmic strands linking adjacent cells for exchange of materials. Cell envelope (bacteria): three layers from outside, the glycocalyx (a loose slime layer or a tough capsule), the cell wall (peptidoglycan) and the plasma membrane, acting together as a protective unit.

Worked example

When fruits ripen, cells separate and the fruit softens. Which layer is broken down and what is it made of?

Try it first, then show the solutionSolution

1. Adjacent plant cells are held together by the middle lamella
2. It is made mainly of calcium pectate, which ripening enzymes break down

Answer: The middle lamella (calcium pectate)

Endomembrane system: ER, Golgi complex, lysosomes and vacuoles

These membrane-bound organelles work in a coordinated way, so they are grouped as the endomembrane system (mitochondria, chloroplasts and peroxisomes are not included). Endoplasmic reticulum (ER): a network of tubules and sacs dividing the cytoplasm into a luminal (inside) and an extraluminal compartment. Rough ER carries ribosomes and makes and secretes proteins; it is extensive in cells secreting enzymes and hormones. Smooth ER lacks ribosomes and makes lipids; in animal cells it makes steroid hormones and also helps detoxify drugs. Golgi complex (described by Camillo Golgi, 1898): stacks of flat, disc-shaped cisternae with a cis (forming) face towards the ER and a trans (maturing) face towards the plasma membrane. It receives vesicles from the ER, modifies, packages and dispatches proteins to their destinations or for secretion, and forms glycoproteins and glycolipids. Lysosomes: membrane-bound vesicles budded off the Golgi, filled with hydrolytic enzymes (lipases, proteases, carbohydrases, nucleases) that work best at an acidic pH; they digest food vacuoles, worn-out organelles and, when the cell dies, the cell itself ('suicide bags'). Vacuoles: membrane-bound spaces with water, sap, excretory products and other materials; the membrane is the tonoplast, which pumps ions in, so their concentration in the vacuole is higher than in cytoplasm. In plant cells a large central vacuole may fill up to 90% of the volume and keeps the cell turgid; contractile vacuoles expel excess water in *Amoeba*; food vacuoles form around engulfed food in protists.

Worked example

A pancreatic acinar cell secretes large quantities of digestive enzymes. Which two organelles would you expect to be very well developed?

Try it first, then show the solutionSolution

1. Enzymes are proteins, made on ribosomes of the rough ER
2. They are then modified and packed into secretory vesicles by the Golgi complex

Answer: Rough endoplasmic reticulum and Golgi complex

Mitochondria, plastids, ribosomes and microbodies

Mitochondria: rod- or sausage-shaped, about 0.2–1.0 µm wide and 1–4 µm long; their number depends on how active the cell is. Double membrane: a smooth outer membrane and an inner membrane folded into cristae, which increase the surface for respiratory enzymes; the space inside, the matrix, holds enzymes of the Krebs cycle, a circular DNA, a few RNA molecules and 70S ribosomes. They are sites of aerobic respiration, producing ATP ('powerhouses'), and divide by fission. Plastids (plant cells and some protists): chloroplasts (green, with chlorophyll and carotenoids; photosynthesis), chromoplasts (fat-soluble carotenoid pigments giving yellow, orange or red colours to flowers and fruits) and leucoplasts (colourless storage plastids: amyloplasts store starch, as in potato; elaioplasts store oils and fats; aleuroplasts store proteins). A chloroplast has a double membrane enclosing the stroma; inside are flattened sacs, thylakoids, stacked into grana and joined by stroma lamellae. Chlorophyll is in the thylakoids; the stroma has enzymes for carbohydrate and protein synthesis, DNA and 70S ribosomes. Ribosomes (first seen by George Palade, 1953): granules of RNA and protein with no membrane; they make proteins. Eukaryotic ribosomes in the cytoplasm are 80S (60S + 40S subunits); prokaryotic ones are 70S (50S + 30S). S is the Svedberg unit, a measure of how fast a particle sediments in a centrifuge, so subunit values do not simply add. Microbodies: small vesicles bounded by a single membrane, carrying enzymes: peroxisomes break down harmful hydrogen peroxide and take part in photorespiration; glyoxysomes in germinating fatty seeds convert fats to carbohydrates.

Worked example

A tomato turns from green to red as it ripens. Which plastid change occurs?

Try it first, then show the solutionSolution

1. Green colour comes from chlorophyll in chloroplasts
2. During ripening chlorophyll breaks down and carotenoid pigments (such as lycopene) build up: chloroplasts change into chromoplasts

Answer: Chloroplasts are converted into chromoplasts

Cytoskeleton, cilia, flagella and centrioles

The cytoskeleton is a network of protein filaments in the cytoplasm that gives mechanical support, maintains shape, and allows movement of the cell and of materials inside it. (1) Microfilaments: thin solid fibres of actin (about 7 nm); involved in cytoplasmic streaming, amoeboid movement, muscle contraction and forming the cleavage furrow. (2) Microtubules: hollow tubes of tubulin (about 25 nm); form the spindle, cilia, flagella and centrioles and act as tracks for vesicles. (3) Intermediate filaments (about 10 nm, e.g. keratin): rope-like fibres giving tensile strength and anchoring the nucleus. Cilia (short, many, beating like oars) and flagella (longer, few, wave-like) are hair-like outgrowths covered by the plasma membrane. Their core, the axoneme, has nine doublets of peripheral microtubules around two central singlets (9 + 2 arrangement), joined by radial spokes and linkers; they grow from a basal body that has the same structure as a centriole. (Prokaryotic flagella are built differently.) Centrosome: in animal cells, a pair of centrioles lying at right angles in an amorphous pericentriolar matter. Each centriole is a cylinder of nine peripheral triplets of tubulin with no central microtubules (9 + 0), linked by protein spokes to a central hub in a cartwheel pattern. Centrioles form the basal bodies of cilia and flagella and organise the spindle in animal cells; higher plants lack them.

Worked example

How many microtubules are in the axoneme of a cilium and in one centriole?

Try it first, then show the solutionSolution

1. Axoneme: 9 doublets × 2 + 2 central singlets = 20
2. Centriole: 9 triplets × 3 = 27; no central microtubules

Answer: 20 in an axoneme; 27 in a centriole

Nucleus and types of chromosomes

The nucleus (first described by Robert Brown) controls the cell's activities. Nuclear envelope: two membranes separated by a perinuclear space (about 10–50 nm); the outer membrane is continuous with the ER and may carry ribosomes; at intervals the two membranes fuse to form nuclear pores, through which RNA and proteins move between nucleus and cytoplasm. Nucleoplasm (nuclear matrix) contains the nucleolus and chromatin. The nucleolus is a spherical body not bounded by a membrane; it is the site of ribosomal RNA synthesis, so it is large in cells making a lot of protein. Chromatin (named by Flemming) is a loose network of DNA with histone and non-histone proteins and some RNA; during division it condenses into chromosomes. Each chromosome has a primary constriction, the centromere, with disc-like kinetochores on its sides where spindle fibres attach. Types by centromere position: metacentric, centromere in the middle, two equal arms; sub-metacentric, centromere slightly away from the middle, one arm shorter; acrocentric, centromere close to one end, one extremely short arm and one very long arm; telocentric, centromere at the very end. Some chromosomes also have a secondary constriction that cuts off a small knob-like piece called the satellite (such chromosomes are SAT chromosomes); a secondary constriction is often the site where the nucleolus forms.

Worked example

A chromosome has arms of 7 µm and 0.5 µm. Classify it.

Try it first, then show the solutionSolution

1. The arms are unequal, so it is not metacentric; there is a short arm, so it is not telocentric
2. The long arm is fourteen times the short arm (7 ÷ 0.5 = 14), so the centromere lies very close to one end, giving one extremely short and one very long arm: acrocentric (in a sub-metacentric chromosome the arms differ much less, and a telocentric one has no short arm at all)

Answer: Acrocentric

Prokaryotic vs eukaryotic cells; plant vs animal cells

Prokaryotic cells (bacteria, cyanobacteria, mycoplasma) are generally smaller (about 1–10 µm). They have no nuclear membrane: genetic material is a single circular DNA lying naked in the cytoplasm as the nucleoid; many also have small circular plasmids. They lack membrane-bound organelles (no mitochondria, ER, Golgi, chloroplasts); ribosomes are 70S; the wall contains peptidoglycan; the membrane may fold into mesosomes that help in wall formation, DNA replication and respiration. Eukaryotic cells (protists, fungi, plants, animals) are larger (about 10–100 µm), with a true nucleus bounded by an envelope, membrane-bound organelles, 80S cytoplasmic ribosomes, linear chromosomes with histones and a cytoskeleton. Plant cells have a cellulose cell wall, plastids and a large central vacuole; centrioles are absent in higher plants; reserve food is starch. Animal cells lack a cell wall and plastids, have small vacuoles, have centrioles; reserve food is glycogen.

Worked example

An electron micrograph shows a cell with 70S ribosomes, a circular DNA lying free in the cytoplasm, a peptidoglycan wall and no mitochondria. Classify it.

Try it first, then show the solutionSolution

1. No nuclear membrane (nucleoid) and no membrane-bound organelles
2. 70S ribosomes and a peptidoglycan wall are bacterial features

Answer: A prokaryotic (bacterial) cell

Cell: The Unit of Life in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Cell Organelles, Nucleus and Cell Comparisons
• Cell Theory, Plasma Membrane and Transport

Cell: The Unit of Life: key facts

Surface area to volume ratio (cube of side a; sphere of radius r)

$\frac{SA}{V}=\frac{6a^2}{a^3}=\frac{6}{a};\frac{SA}{V}=\frac{4\pi r^2}{\frac{4}{3}\pi r^3}=\frac{3}{r}$

The ratio falls as a cell grows: one reason cells stay small.

Real size from a micrograph

$\text{real size}=\frac{\text{image size}}{\text{magnification}}$

Convert units first: 1 mm = 1000 µm.

Ribosome types

$80S=60S+40S(\text{eukaryotes});70S=50S+30S(\text{prokaryotes, mitochondria, chloroplasts})$

S values are sedimentation rates and are not additive.

Microtubule patterns

$\text{cilium/flagellum axoneme}=9+2;\text{centriole, basal body}=9+0\text{ (triplets)}$

Axoneme: 9 doublets + 2 singlets = 20 microtubules.

Na⁺/K⁺ pump

$3N{a}^{+}\text{out}+2K^{+}\text{in per ATP}$

Active transport against both gradients; an antiport.

Cell: The Unit of Life: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Cell: The Unit of Life

The question patterns to expect, and the method that works for each.

Tricks to remember Cell: The Unit of Life

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Hooke Looked, Leeuwen Lived, Brown Nucleus, SS Theory, Virchow Origin

  Hooke named cells, Leeuwenhoek saw living cells, Brown found the nucleus, Schleiden and Schwann gave the theory, Virchow said cells come from cells.

  Use it when: History of cell theory.

• Uni-Sym-Anti

  Uni = one alone; Sym = same way together; Anti = against each other.

  Use it when: Carrier types.

• Rough makes protein, Smooth makes steroid

  Ribosomes on RER = proteins; SER = lipids and steroids.

  Use it when: Types of ER.

• Amylo-Elaio-Aleuro = Starch-Oil-Protein

  Amylum (starch), elaion (oil), aleuron (flour, protein).

  Use it when: Leucoplasts.

• Meta-Sub-Acro-Telo: middle, slightly off, near end, at end

  The centromere slides from the middle to the tip.

  Use it when: Chromosome types.

Cell: The Unit of Life: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section D style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 5-mark question split into 1 + 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Cell: The Unit of Life

The slips examiners see most often, and what to write instead.

• ✗Mistake: Adding Svedberg units

  Students treat S as a mass.

  Wrong working

  60S + 40S = 100S.

  Right working

  60S and 40S subunits form an 80S ribosome; S measures sedimentation rate, which is not additive.

  ✓Do this: Learn 80S (60 + 40) and 70S (50 + 30) as fixed facts.

  Usually costs: 1 mark.

• ✗Mistake: Calling facilitated diffusion active transport

  Both use proteins.

  Wrong working

  Glucose enters RBCs by active transport using a carrier.

  Right working

  It is facilitated diffusion: carrier-mediated but down the gradient and without ATP.

  ✓Do this: Ask: against the gradient? ATP used?

  Usually costs: 1 mark.

• ✗Mistake: Wrong microtubule formula

  Axoneme and centriole patterns are swapped.

  Wrong working

  Centrioles have a 9 + 2 arrangement.

  Right working

  Cilia and flagella: 9 + 2 (doublets); centrioles: 9 + 0 (triplets).

  ✓Do this: Centriole has no centre.

  Usually costs: 1 mark.

• ✗Mistake: Including mitochondria in the endomembrane system

  They are membrane-bound.

  Wrong working

  ER, Golgi, lysosomes, vacuoles and mitochondria form the endomembrane system.

  Right working

  Mitochondria, chloroplasts and peroxisomes work independently and are excluded.

  ✓Do this: Endomembrane = ER, Golgi, lysosomes, vacuoles.

  Usually costs: 1 mark.

• ✗Mistake: Saying the nucleolus has a membrane

  It looks like a separate body.

  Wrong working

  The nucleolus is bounded by a single membrane.

  Right working

  The nucleolus is not membrane-bound; it is a dense region of rRNA synthesis.

  ✓Do this: Nucleolus = no membrane.

  Usually costs: 1 mark.

Practice questions on Cell: The Unit of Life

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   The smallest known cells are:
   (a) bacteria
   (b) Mycoplasma
   (c) viruses
   (d) red blood cells

   Hint

   About 0.3 µm.

   Answer

   (b)

2. Q2 · 1 mark · MCQExam level

   Glyoxysomes are found in:
   (a) animal liver cells
   (b) germinating oily seeds
   (c) red blood cells
   (d) bacteria

   Hint

   Fat to sugar.

   Answer

   (b)

3. Q3 · 1 mark · Very short answerExam level

   Who stated that new cells arise from pre-existing cells?

   Hint

   1855.

   Answer

   Rudolf Virchow

4. Q4 · 1 mark · Very short answerExam level

   Name the plastid that stores oils.

   Hint

   Elaion.

   Answer

   Elaioplast

5. Q5 · 2 marks · Short answerExam level

   What are plasmodesmata? State their function.

   Hint

   Through walls.

   Answer

   Fine cytoplasmic strands passing through the cell walls and middle lamella of adjacent plant cells; they connect the cytoplasm of neighbouring cells for exchange of materials.

6. Q6 · 2 marks · Short answerHarder exam level

   Distinguish between metacentric and acrocentric chromosomes.

   Hint

   Centromere position.

   Answer

   Metacentric: centromere in the middle, two equal arms (V-shaped at anaphase). Acrocentric: centromere close to one end, one very short and one very long arm (J-shaped).

7. Q7 · 2 marks · Short answerHarder exam level

   Distinguish between active and passive transport.

   Hint

   Gradient and ATP.

   Answer

   Passive transport moves substances down a concentration gradient without ATP (diffusion, osmosis, facilitated diffusion). Active transport moves them against the gradient using ATP and carrier proteins (Na⁺/K⁺ pump).

8. Q8 · 3 marks · Short answerHarder exam level

   Describe the structure of a chloroplast.

   Hint

   Double membrane, grana.

   Answer

   A double membrane encloses the stroma. Flattened membranous sacs, thylakoids, are stacked into grana, joined by stroma lamellae; chlorophyll is in the thylakoid membranes. The stroma contains enzymes for carbohydrate and protein synthesis, circular DNA, 70S ribosomes and starch grains.

9. Q9 · 3 marks · Short answerHarder exam level

   Describe the structure of the nucleus.

   Hint

   Envelope, pores, nucleolus, chromatin.

   Answer

   Double nuclear envelope with a perinuclear space, the outer membrane continuous with the ER; nuclear pores where the membranes fuse; nucleoplasm with a non-membranous nucleolus (rRNA synthesis); chromatin of DNA, histones, non-histone proteins and RNA that condenses into chromosomes during division.

10. Q10 · 3 marks · Short answerHarder exam level

    Give four differences between plant and animal cells.

    Hint

    Wall, plastids, vacuole, centrioles.

    Answer

    Plant cells have a cellulose cell wall, plastids, a large central vacuole and store starch; animal cells lack a wall and plastids, have small vacuoles, store glycogen and have centrioles (absent in higher plants).

11. Q11 · 5 marks · Long answerHarder exam level

    (a) Describe the structure of cilia and flagella. [3]
    (b) Describe the structure of a centriole and state its function. [2]

    Hint

    9 + 2 and 9 + 0.

    Answer

    (a) Hair-like outgrowths covered by plasma membrane; core axoneme with nine peripheral doublets of microtubules and two central singlets (9 + 2) in a central sheath, joined by radial spokes and linkers; arise from a basal body. Cilia short and many; flagella long and few. (b) A cylinder of nine peripheral triplet microtubules with a cartwheel of spokes to a central hub (9 + 0); a pair lies at right angles in the centrosome. Forms basal bodies of cilia and flagella and the spindle in animal cells.

12. Q12 · 5 marks · Long answerHarder exam level

    (a) Describe the endomembrane system and explain why it is called a system. [3]
    (b) Why are lysosomes rich in acid hydrolases? [2]

    Hint

    Coordinated functions.

    Answer

    (a) ER, Golgi complex, lysosomes and vacuoles; their functions are coordinated: proteins and lipids made in the ER travel in vesicles to the Golgi, where they are modified and packaged into lysosomes, vacuoles or secretory vesicles. (b) Their job is intracellular digestion of food particles, worn-out organelles and macromolecules; their hydrolases work best at the acidic pH inside the lysosome, which also protects the cytoplasm if a lysosome leaks.

13. Q13 · 2 marks · Short answerHarder exam level

    Under a microscope set at ×2000, a cell appears 20 mm long. What is its real length in micrometres?

    Hint

    Image ÷ magnification.

    Answer

    20 mm ÷ 2000 = 0.01 mm = 10 µm.

14. Q14 · 3 marks · Short answerHOTS / competency

    In a liver cell treated with a poison that stops ATP production, the cell begins to gain Na⁺ and lose K⁺. Explain using membrane transport.

    Hint

    Pump stops.

    Answer

    The Na⁺/K⁺ pump uses ATP to push 3 Na⁺ out and bring 2 K⁺ in against their gradients. Without ATP the pump stops, but Na⁺ keeps leaking in and K⁺ keeps leaking out down their gradients by passive transport, so the gradients run down.

15. Q15 · 3 marks · Short answerHOTS / competency

    A biologist claims that mitochondria and chloroplasts were once free-living bacteria. Give three structural features from this chapter that support the claim.

    Hint

    Compare with prokaryotes.

    Answer

    Both have their own circular DNA, like bacteria; both have 70S ribosomes, like prokaryotes; both divide by fission and have a double membrane, the inner one possibly from the original bacterium.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Fluid mosaic model was given by?Show answer

   Singer and Nicolson (1972).

2. 2.Material of middle lamella?Show answer

   Calcium pectate.

3. 3.Membrane of the vacuole?Show answer

   Tonoplast.

4. 4.Folds of inner mitochondrial membrane?Show answer

   Cristae.

5. 5.Stacks of thylakoids?Show answer

   Grana.

6. 6.Ribosome of prokaryotes?Show answer

   70S (50S + 30S).

7. 7.Protein of microfilaments?Show answer

   Actin.

8. 8.Site of rRNA synthesis?Show answer

   Nucleolus.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you name five scientists and their contribution to cell theory?
• ☐Can you draw the fluid mosaic model?
• ☐Can you explain uniport, symport and antiport with examples?
• ☐Can you describe the Golgi complex and its functions?
• ☐Can you draw a mitochondrion and a chloroplast?
• ☐Can you state the 9 + 2 and 9 + 0 patterns?
• ☐Can you classify chromosomes by centromere position?
• ☐Can you give four differences between prokaryotic and eukaryotic cells?

Cell: The Unit of Life: frequently asked questions