Class 9 BiologyChapter 2Revise
Revise the cell
29 flashcards that come back when due, 18 practice questions in exam styles, and one page to print.
Flashcards
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Limit of resolution of the human eye?
0.1 mm, seen from about 25 cm (the near point). Closer points merge into one.
Who first saw cells, when, and in what?
Robert Hooke, 1665, in a thin slice of cork, with a microscope he designed (about 200 to 300X).
Total magnification with a 10X eyepiece and a 40X objective?
400X. Multiply the two powers.
How do you estimate the size of a cell under a microscope?
Diameter of the field of view in µm ÷ number of cells across it.
What does an electron microscope use instead of light?
A beam of electrons. It shows details down to the nanometre scale.
What does selectively permeable mean?
It lets some substances pass through and blocks others. The cell membrane is selectively permeable.
Define osmosis.
Movement (diffusion) of water through a selectively permeable membrane, from a dilute solution to a concentrated one.
A cell in a hypotonic solution will...
Swell. The outside has less solute than the inside, so more water enters than leaves.
A cell in a hypertonic solution will...
Shrink. The outside has more solute, so more water leaves than enters.
Fluid mosaic model in one line?
A lipid bilayer (heads out, tails in) with proteins set in it; molecules move sideways, flip and rotate.
How thick is the cell membrane?
About 7 to 10 nanometres.
Main material of the plant cell wall?
Cellulose, a carbohydrate made of many glucose units. In our diet it acts as roughage.
Cell wall or cell membrane: which is selectively permeable?
The membrane. The wall is freely permeable to water and dissolved minerals.
Two features of a prokaryotic cell?
No well-defined nucleus (DNA in the nucleoid) and no membrane-bound organelles. Example: bacteria.
Typical size of prokaryotic and eukaryotic cells?
Prokaryotic 1 to 10 µm; eukaryotic 10 to 100 µm.
What happens in the nucleolus?
Ribosome subunits are made. They leave through nuclear pores and join in the cytoplasm.
What is a gene?
A functional segment of DNA, carrying information for a character.
RER versus SER?
RER has ribosomes, makes and secretes proteins. SER has none, makes and stores fats and hormones.
The cell's post office?
The Golgi apparatus: modifies, sorts and packs proteins and lipids into vesicles.
What do lysosomes do?
Their enzymes break down waste and worn out parts; the products are reused.
Energy currency of the cell, and where it is made?
ATP, made in mitochondria during cellular respiration.
Which organelles have their own DNA, apart from the nucleus?
Mitochondria and chloroplasts (plastids). They also have their own ribosomes.
Chloroplast, chromoplast, leucoplast?
Green, makes food. Coloured (yellow, orange, red), in petals and fruits. Colourless, stores starch, oil or protein.
Result of mitosis?
Two daughter cells, genetically identical to the parent, with the same number of chromosomes.
Result of meiosis?
Four cells, each with half the number of chromosomes. Two divisions, one after the other.
Where does meiosis happen?
Only in reproductive organs: testes and ovaries in animals; anthers and ovaries in flowering plants.
The three points of cell theory?
All living things are made of one or more cells. The cell is the basic unit of structure and function. All cells come from pre-existing cells.
Contact inhibition?
Many animal cells stop dividing when they touch neighbours. Cancer cells lose this and form tumours.
Totipotency, and who proposed it?
A living plant cell can grow into a whole plant under the right conditions. Gottlieb Haberlandt, 1902.
Practice questions
Questions in the styles CBSE uses: multiple choice, assertion and reason, case based and labelling a diagram. Each answer comes with the reason. Send any question to a friend; the link opens it here and carries nothing about you.
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1Multiple choice Studying cells
A microscope has a 15X eyepiece and a 40X objective. What is its total magnification?
The powers multiply: 15 × 40 = 600X.
Show the answer
C. The powers multiply: 15 × 40 = 600X.
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2Multiple choice Studying cells
The field of view is 2.5 mm wide and 50 cells fit across it. How big is one cell?
2.5 mm = 2500 µm, and 2500 ÷ 50 = 50 µm.
Show the answer
B. 2.5 mm = 2500 µm, and 2500 ÷ 50 = 50 µm.
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3Multiple choice Cell membrane
A slice of cucumber goes limp after being sprinkled with salt for twenty minutes. The best explanation is:
The salty layer outside is hypertonic, so water moves out of the cells through their membranes and they lose firmness.
Show the answer
B. The salty layer outside is hypertonic, so water moves out of the cells through their membranes and they lose firmness.
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4Multiple choice Cell membrane
Red blood cells are kept in a solution and neither swell nor shrink. The solution is:
No net change means water moves in and out equally: the solute concentration is the same inside and outside.
Show the answer
C. No net change means water moves in and out equally: the solute concentration is the same inside and outside.
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5Multiple choice Cell wall and cell types
Which of these is present in a bacterial cell?
Bacteria have a cell wall, membrane, cytoplasm, ribosomes and a nucleoid, but no membrane-bound organelles or nuclear membrane.
Show the answer
D. Bacteria have a cell wall, membrane, cytoplasm, ribosomes and a nucleoid, but no membrane-bound organelles or nuclear membrane.
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6Multiple choice Cell organelles
A slice of raw potato turns blue black with iodine. Which plastid stored what it detected?
Iodine shows starch, and in potato cells starch is stored in colourless leucoplasts.
Show the answer
C. Iodine shows starch, and in potato cells starch is stored in colourless leucoplasts.
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7Multiple choice Cell organelles
An organelle has two membranes, the inner one folded into finger-like projections. It is the:
Folds of the inner membrane are cristae, found in mitochondria, where they give more surface for energy release.
Show the answer
B. Folds of the inner membrane are cristae, found in mitochondria, where they give more surface for energy release.
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8Multiple choice Cell division
Which cells in a flowering plant divide by meiosis?
Meiosis happens only in reproductive organs: anthers make pollen grains and ovaries make egg cells.
Show the answer
B. Meiosis happens only in reproductive organs: anthers make pollen grains and ovaries make egg cells.
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9Multiple choice Cell theory
Which scientist added to cell theory that new cells arise only from pre-existing cells?
Rudolf Virchow, 1855.
Show the answer
C. Rudolf Virchow, 1855.
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10Assertion and reason Cell wall and cell types
Assertion (A) An onion peel cell placed in strong sugar solution keeps its outline, though its contents shrink.
Reason (R) The plant cell wall is rigid and holds its shape while the membrane pulls away.
Both are true, and the rigid wall is exactly why the outline stays.
Show the answer
A. Both are true, and the rigid wall is exactly why the outline stays.
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11Assertion and reason Cell membrane
Assertion (A) Osmosis can take place without any membrane.
Reason (R) Diffusion is the net movement of particles from a region of higher to lower concentration.
Osmosis by definition needs a selectively permeable membrane, so A is false. R, the definition of diffusion, is true.
Show the answer
D. Osmosis by definition needs a selectively permeable membrane, so A is false. R, the definition of diffusion, is true.
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12Assertion and reason Cell organelles
Assertion (A) Mature human red blood cells cannot divide.
Reason (R) Mature red blood cells have no nucleus.
Without a nucleus they cannot repair or divide, so they live only about 120 days. R explains A.
Show the answer
A. Without a nucleus they cannot repair or divide, so they live only about 120 days. R explains A.
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13Assertion and reason Cell organelles
Assertion (A) Mitochondria are called the powerhouses of the cell.
Reason (R) Mitochondria have their own DNA and ribosomes.
Both are true, but the name comes from energy release as ATP, not from having DNA.
Show the answer
B. Both are true, but the name comes from energy release as ATP, not from having DNA.
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14Assertion and reason Cell division
Assertion (A) Meiosis helps create variation among offspring.
Reason (R) Meiosis takes place in all the cells of the body.
A is true. R is false: meiosis happens only in cells of the reproductive organs.
Show the answer
C. A is true. R is false: meiosis happens only in cells of the reproductive organs.
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15Case based Cell membrane
The raisin test
Meera put ten raisins of the same size in a bowl of plain water and another ten in a bowl of thick sugar syrup. She left both overnight. In the morning the raisins in water were plump and smooth; those in syrup had hardly changed and looked slightly more wrinkled.
(i) Why did the raisins in plain water swell?
Plain water is hypotonic compared with the sugary cell contents, so water moved in.
Show the answer
B. Plain water is hypotonic compared with the sugary cell contents, so water moved in.
(ii) Compared with the inside of the raisin cells, the thick syrup is:
The syrup has more solute than the cells, so it is hypertonic and draws water out.
Show the answer
C. The syrup has more solute than the cells, so it is hypertonic and draws water out.
(iii) Why did Meera use raisins of the same size in both bowls?
Keeping everything the same except the liquid lets any difference be put down to osmosis.
Show the answer
A. Keeping everything the same except the liquid lets any difference be put down to osmosis.
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16Case based Cell organelles
A cell that ships proteins
Cells of a digestive gland make large amounts of an enzyme, which is a protein, and release it out of the cell. Under an electron microscope these cells are packed with membranes studded with tiny granules, and with many stacks of flattened sacs near the cell surface.
(i) The membranes studded with granules are most likely:
Ribosomes on the ER make it rough; RER makes and secretes proteins.
Show the answer
B. Ribosomes on the ER make it rough; RER makes and secretes proteins.
(ii) The stacks of flattened sacs are the:
Stacks of flat sacs form the Golgi apparatus, which packs proteins into vesicles.
Show the answer
A. Stacks of flat sacs form the Golgi apparatus, which packs proteins into vesicles.
(iii) Which order does the enzyme follow on its way out?
Made on ribosomes of the RER, carried through the ER, packed by the Golgi into vesicles, released at the membrane.
Show the answer
B. Made on ribosomes of the RER, carried through the ER, packed by the Golgi into vesicles, released at the membrane.
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17Label the diagram Cell organelles
Label the parts of this plant cell.
The wall is the outermost layer, with the membrane just inside it. The big central space is the vacuole; green bodies are chloroplasts and the small capsules with folds are mitochondria.
Show the answer
1: Cell wall, 2: Cell membrane, 3: Nucleus, 4: Vacuole, 5: Chloroplast, 6: Mitochondrion. The wall is the outermost layer, with the membrane just inside it. The big central space is the vacuole; green bodies are chloroplasts and the small capsules with folds are mitochondria.
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18Label the diagram Cell organelles
Label the parts of this mitochondrion.
Two membranes: a smooth outer one and an inner one folded into cristae. Stroma belongs to the chloroplast, not the mitochondrion.
Show the answer
1: Outer membrane, 2: Inner membrane, 3: Cristae. Two membranes: a smooth outer one and an inner one folded into cristae. Stroma belongs to the chloroplast, not the mitochondrion.
Memory aids
Memory aid
Ladder of a thousand
m, mm, µm, nm
Each step down is a thousand times smaller. 1 mm = 1000 µm, 1 µm = 1000 nm.
Memory aid
Hypo makes a hippo
Hypo swells, hyper shrinks, iso stays
Name the solution outside the cell. Hypotonic: water rushes in and the cell fattens like a hippo.
Memory aid
Pro is before, eu is true
Prokaryote: before a nucleus. Eukaryote: a true nucleus.
Bacteria are prokaryotic; plant and animal cells are eukaryotic.
Memory aid
Rough has the riders
RER: ribosomes, proteins. SER: synthesis and storage of fats and hormones.
The ribosomes riding on the ER make it look rough.
Memory aid
Chloro, chromo, leuco
Green cook, colour box, white larder
Chloroplasts make food, chromoplasts colour petals and fruits, leucoplasts store starch, oils or proteins.
Memory aid
Twins and quarters
Mitosis: 2 twins, full set. Meiosis: 4 cells, half set each.
Mitosis copies, meiosis halves. Fertilisation puts two halves back together.
Memory aid
Plants, animals, parents
Schleiden 1838, Schwann 1839, Virchow 1855
Plants are made of cells, animals too, and every cell has a parent cell.
One page summary
One page summary
Class 9 Biology, Chapter 2: Cell: The Building Block of Life
Everything in the chapter on one page.
Seeing cells (2.1)
- Eye resolves 0.1 mm at 25 cm.
- Hooke, 1665, cork, named cells.
- Magnification = eyepiece × objective.
- Cell size = field (µm) ÷ cells across.
- Electron microscope: electron beam, nm detail.
- Better microscopes: resolution, contrast, magnification.
Membrane and osmosis (2.2.1)
- Membrane = plasma membrane, selectively permeable.
- Osmosis: water across a selectively permeable membrane, dilute to concentrated.
- Hypotonic: swells. Isotonic: no change. Hypertonic: shrinks.
- Lipid bilayer + proteins, 7 to 10 nm, fluid mosaic model.
Wall and cell types (2.2.2, 2.3)
- Wall: rigid, permeable, mostly cellulose (plants).
- Walls in plants, fungi, bacteria; none in animals.
- In strong sugar: plant contents pull from wall; animal cell shrinks.
- Prokaryotic: nucleoid, no membrane-bound organelles, 1 to 10 µm.
- Eukaryotic: true nucleus, organelles, 10 to 100 µm.
Organelles (2.3.1)
- Nucleus: DNA in chromosomes; nucleolus makes ribosome subunits.
- Ribosome: proteins. RER: proteins. SER: fats, hormones.
- Golgi: pack and ship. Lysosome: break down waste.
- Mitochondria: energy as ATP, cristae, own DNA.
- Plastids: chloro (food), chromo (colour), leuco (store).
- Vacuole: cell sap, keeps plant cell firm.
Division (2.4, 2.4.1)
- Root tip cells show stages of division (Activity 2.5).
- Mitosis: 2 identical cells, same chromosome number.
- Meiosis: 2 divisions, 4 cells, half the chromosomes.
- Meiosis only in testes, ovaries, anthers.
- Errors: tumours (mitosis), genetic disorders (meiosis).
Cell theory (2.5, 2.5.1)
- Schleiden 1838 plants, Schwann 1839 animals, Virchow 1855.
- All life is cells; cell is the unit; cells from cells.
- Every cell has a life span.
- Contact inhibition; cancer cells lose it.
- Haberlandt 1902: totipotency, plant tissue culture.
numford.com. Section numbers follow NCERT Exploration, Grade 9; the wording is our own.