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Unit notes and practice questions

Grade 9 Biology unit 3: Cells

Everything here is for unit 3 of the Grade 9 Biology textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.

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10
Practice questions on unit 3
44–73
The textbook pages for unit 3

Short notes for unit 3

The cards filed under this chapter on the Grade 9 Biology page. Open one at a time.

Transport MechanismConcentration GradientEnergy (ATP) RequiredExample
DiffusionHigh to low concentrationNoOxygen entering cells
OsmosisHigh water to low water concentrationNoWater entry into plant roots
Active transportLow to high concentrationYesSodium-potassium pump

When you use it

Use to classify how substances cross cell membranes based on gradient direction and energy input.

Watch out

Active transport moves substances against the concentration gradient and always requires respiratory energy.

Drafted from Grade 9 Biology, pages 44-73, then checked twice before it went up

When you use it

Use when predicting the physical response of cells placed in hypotonic, isotonic, or hypertonic solutions.

Watch out

Plant cells do not burst in hypotonic solutions because the rigid cellulose cell wall exerts wall pressure, making the cell turgid. Animal cells lack a cell wall and burst (lysis).

Drafted from Grade 9 Biology, pages 44-73, then checked twice before it went up

Organelle or StructurePlant CellAnimal Cell
Cell wallPresent (Cellulose)Absent
ChloroplastPresentAbsent
VacuoleLarge and permanentSmall and temporary
CentriolesAbsentPresent

When you use it

Use to distinguish plant and animal cells under a microscope or identify cell-specific organelles.

Watch out

Mitochondria and plasma membranes exist in both plant and animal cells, not only in animal cells.

Drafted from Grade 9 Biology, pages 44-73, then checked twice before it went up

When you use it

Use when stating the core principles of cell theory or identifying the historical contributions of early cell biologists.

Watch out

Robert Hooke observed and named cork cells in 1665, but Schleiden (plants, 1838), Schwann (animals, 1839), and Virchow (pre-existing cells, 1856) formulated the cell theory.

Drafted from Grade 9 Biology, pages 44-73, then checked twice before it went up

FeatureProkaryotic CellEukaryotic Cell
NucleusAbsentPresent
Membrane-bound organellesAbsentPresent
RibosomesRelatively smallRelatively large
DNA organizationCircular plasmids, no proteinsLinear strands with proteins
Cell wallPeptidoglycanCellulose in plants, absent in animals

When you use it

Use to compare structural complexity and distinguish bacteria from plant and animal cells.

Watch out

Ribosomes are present in both prokaryotes and eukaryotes. Do not list ribosomes as membrane-bound organelles.

Drafted from Grade 9 Biology, pages 44-73, then checked twice before it went up

OrganelleWhat it does
NucleusHolds the chromosomes (DNA) and controls the cell's activities, directing which proteins are made.
MitochondrionSite of aerobic respiration, where most of the cell's ATP is released. Plant cells hold mitochondria just as animal cells do.
RibosomeSite of protein synthesis. Found free in the cytoplasm or attached to the rough endoplasmic reticulum.
Endoplasmic reticulum (ER)A network of membrane channels that carries materials through the cell. Rough ER carries ribosomes and handles proteins; smooth ER has no ribosomes and makes lipids.
Golgi apparatusModifies, sorts and packages the proteins arriving from the ER into vesicles, for use inside the cell or for secretion.
LysosomeA sac of digestive enzymes that breaks down worn out cell parts, food particles and invading bacteria.
ChloroplastContains chlorophyll and is the site of photosynthesis. Plant and algal cells have it, animal cells never do, and even in a plant the cells that never meet light, such as root cells, have none.
VacuoleIn a plant cell one large permanent vacuole stores cell sap, and its water pressure keeps the cell turgid. Animal cells have small temporary vacuoles.

When you use it

Use when a question names an organelle and asks for its job, or describes a job and asks which organelle does it. It also settles which parts a plant cell and an animal cell share when you are asked to compare the two.

Watch out

Students write that a plant cell has chloroplasts instead of mitochondria, then answer that a plant respires in its chloroplast. A plant cell has both. It respires in its mitochondria day and night, exactly as an animal cell does, while the chloroplast works only in the light and only the green cells that reach the light carry one at all. If a question asks which organelle a plant cell and an animal cell share, mitochondrion, nucleus, ribosome and cell membrane are all correct; chloroplast, cell wall and the large vacuole are not.

Practice questions on unit 3

10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.

Question 1

Which scientist first used the word cell in 1665 after observing thin slices of cork?

  1. A.Robert Hooke
  2. B.Anton van Leeuwenhoek
  3. C.Matthias Schleiden
  4. D.Rudolf Virchow
Show the answer and why

Answer: A Robert Hooke

Why

Robert Hooke was the first scientist to observe cells and name the regular pore-like structures cells in 1665 after examining cork under a microscope.

Question 2

What is the primary function of ribosomes in a cell?

  1. A.To synthesize proteins
  2. B.To store water and minerals
  3. C.To release digestive enzymes
  4. D.To trap sunlight for photosynthesis
Show the answer and why

Answer: A To synthesize proteins

Why

Ribosomes are small cellular structures found in large numbers in all cells, and their main function is to synthesize proteins.

Question 3

Which organelle is described as the powerhouse of the cell because it is the site of cellular respiration?

  1. A.Golgi apparatus
  2. B.Mitochondrion
  3. C.Lysosome
  4. D.Rough endoplasmic reticulum
Show the answer and why

Answer: B Mitochondrion

Why

Mitochondria are known as the powerhouse of the cell because their inner folds host chemical reactions of respiration to release energy.

Question 4

What is the term for the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient without using energy?

  1. A.Active transport
  2. B.Diffusion
  3. C.Phagocytosis
  4. D.Osmoregulation
Show the answer and why

Answer: B Diffusion

Why

Diffusion is passive transport where molecules move down their concentration gradient from high to low concentration without an input of energy.

Question 5

Which cellular structure is found in animal cells during cell division but is absent in plant cells?

  1. A.Centriole
  2. B.Chloroplast
  3. C.Cell wall
  4. D.Large central vacuole
Show the answer and why

Answer: A Centriole

Why

Plant cells possess cell walls, chloroplasts, and large permanent vacuoles, while centrioles are found specifically in animal cells.

Question 6

During a biology laboratory class in Hawassa, students prepare a temporary slide of human cheek cells. Which dye is used to stain these animal cells?

  1. A.Iodine solution
  2. B.Methylene blue dye
  3. C.Absolute alcohol
  4. D.Salt solution
Show the answer and why

Answer: B Methylene blue dye

Why

Methylene blue dye is used to stain animal cheek cells so that cellular parts like the nucleus become clearly visible under a light microscope.

Question 7

How does the cell wall of a bacterium (prokaryote) differ from the cell wall of a plant cell (eukaryote)?

  1. A.Bacterial cell walls are made of peptidoglycan, while plant cell walls are made of cellulose.
  2. B.Bacterial cell walls are made of cellulose, while plant cell walls are made of peptidoglycan.
  3. C.Bacterial cell walls are made of chitin, while plant cell walls are made of proteins.
  4. D.Bacterial cell walls are made of lipids, while plant cell walls have no rigid structure.
Show the answer and why

Answer: A Bacterial cell walls are made of peptidoglycan, while plant cell walls are made of cellulose.

Why

According to the textbook comparison table, prokaryotic cell walls are primarily made of peptidoglycan, whereas plant cell walls are always composed of cellulose.

Question 8

Which list correctly shows the hierarchy of biological organization in multicellular organisms from simplest to most complex?

  1. A.Organism → System → Tissue → Organ → Cell
  2. B.Cell → Tissue → Organ → System → Organism
  3. C.Tissue → Cell → Organ → System → Organism
  4. D.Cell → Organ → Tissue → Organism → System
Show the answer and why

Answer: B Cell → Tissue → Organ → System → Organism

Why

In complex organisms, cells form tissues, tissues form organs, organs group into organ systems, and all systems together form the complete organism.

Question 9

What happens to a red blood cell when it is placed into a hypotonic solution?

  1. A.Water leaves the cell, causing it to shrink.
  2. B.The cell wall exerts pressure and keeps the cell turgid.
  3. C.Water enters the cell by osmosis until it swells and bursts.
  4. D.Contractile vacuoles pump out the excess salt molecules.
Show the answer and why

Answer: C Water enters the cell by osmosis until it swells and bursts.

Why

Animal cells lack a rigid cell wall. In a hypotonic solution, water constantly enters the red blood cell by osmosis, causing it to swell and eventually burst (hemolysis).

Question 10

Which of the following is an example of active transport in living organisms?

  1. A.Movement of oxygen into cells for respiration
  2. B.Uptake of mineral ions by root hair cells against a concentration gradient
  3. C.Evaporation of water molecules from leaf surfaces
  4. D.Diffusion of carbon dioxide out of animal tissues
Show the answer and why

Answer: B Uptake of mineral ions by root hair cells against a concentration gradient

Why

Active transport uses energy released during respiration to move substances against a concentration gradient, such as ion uptake by plant root hairs and glucose uptake by villi.

The app holds 12 questions on this unit, marked as you go. These are the first 10.

The textbook pages for unit 3

Unit 3 runs from page 44 to page 73 of the Ministry of Education edition.

Ministry of Education edition, English, 165 pages

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All Grade 9 Biology short notes

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