Science - Grade 8 - QED - Free Printable
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Step-by-step solution for: Science - Grade 8 - QED
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Step-by-step solution for: Science - Grade 8 - QED
Here is the completed and explained worksheet for Chapter 7-3: Cell Boundaries:
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- Regulates what enters and exits the cell
- Provides protection and support (or "maintains homeostasis")
> ✔ *Explanation:* The cell membrane acts as a selective barrier, allowing necessary substances in and out while keeping harmful ones out. It also helps maintain the cell’s internal environment.
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Answer: Protein
> ✔ *Explanation:* Proteins are embedded within the phospholipid bilayer and serve various roles such as transport, signaling, and recognition.
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Answer: Because it is made up of many different types of molecules (like proteins, lipids, carbohydrates) arranged in a patchwork pattern.
> ✔ *Explanation:* The fluid mosaic model describes the membrane as a dynamic structure where proteins float in a sea of lipids—like tiles in a mosaic.
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a. Lipid bilayer → The double layer of phospholipids forming the main structure
b. Protein channel → A protein that spans the membrane with a pore (often shown as a tube-like structure)
c. Carbohydrate chains → Chains attached to the outer surface of the membrane (usually on glycoproteins or glycolipids)
> ✔ *Labeling Guide:*
- Lipid bilayer: The two layers of round circles (phospholipids)
- Protein channel: The large oval or tunnel-shaped structures going through the bilayer
- Carbohydrate chains: Branched structures extending outward from the top of the membrane
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Answer: Plants, fungi, and bacteria
> ✔ *Explanation:* These organisms have rigid cell walls outside their cell membranes for structural support.
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Answer: To provide structural support and protection to the cell.
> ✔ *Explanation:* The cell wall prevents the cell from bursting under osmotic pressure and maintains shape.
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Answer: Cellulose
> ✔ *Explanation:* Plant cell walls are primarily made of cellulose, a strong polysaccharide that gives rigidity to plant cells.
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Answer: Control / Regulate, substances (or molecules)
> ✔ *Explanation:* The membrane selectively allows certain molecules to pass through, maintaining balance inside the cell.
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Answer: Mixture
> ✔ *Explanation:* A solution consists of a solvent (like water) and solutes (dissolved substances).
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Answer: The movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached.
> ✔ *Explanation:* This passive process occurs due to random molecular motion.
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Answer: Equilibrium
> ✔ *Explanation:* At equilibrium, there is no net movement of particles because concentrations are equal.
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Answer: Random, does not
> ✔ *Explanation:* Diffusion is passive—it uses kinetic energy from molecules but doesn't require ATP.
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## OSMOSIS
Answer: Permeable (to that substance)
> ✔ *Explanation:* Permeability refers to the ability of a substance to pass through the membrane.
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Answer: The diffusion of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
> ✔ *Explanation:* Osmosis specifically involves water movement due to concentration differences.
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Hypertonic means
Hypotonic means
Answers:
- Isotonic: Equal concentration of solutes on both sides of the membrane
- Hypertonic: Higher solute concentration outside the cell than inside
- Hypotonic: Lower solute concentration outside the cell than inside
> ✔ *Explanation:* These terms describe the relative solute concentrations between the cell and its environment.
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Answer: Osmosis, swollen (or turgid)
> ✔ *Explanation:* Freshwater is hypotonic to cells, so water moves in by osmosis. Animal cells may burst (lyse), but plant/bacteria cells don’t due to cell walls.
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Answer: Cell wall
> ✔ *Explanation:* The rigid cell wall resists the inward pressure caused by water entering via osmosis.
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## FACILITATED DIFFUSION
Answer: Transport proteins (or carrier proteins)
> ✔ *Explanation:* These proteins help polar or large molecules move across the membrane without using energy.
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Answer: Facilitated diffusion
> ✔ *Explanation:* This is a type of passive transport that uses proteins to speed up the movement of substances down their concentration gradient.
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This worksheet covers key concepts about:
- Structure and function of the cell membrane
- Diffusion and osmosis
- Tonicity (isotonic, hypertonic, hypotonic)
- Facilitated diffusion
- Role of cell walls in plants, fungi, and bacteria
All answers are based on standard biology curriculum content.
Let me know if you'd like this formatted as a printable PDF or need help labeling the diagram!
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1. Name two functions of the cell membrane:
- Regulates what enters and exits the cell
- Provides protection and support (or "maintains homeostasis")
> ✔ *Explanation:* The cell membrane acts as a selective barrier, allowing necessary substances in and out while keeping harmful ones out. It also helps maintain the cell’s internal environment.
---
2. The cell membrane contains ________ molecules that are embedded in the lipid bilayer.
Answer: Protein
> ✔ *Explanation:* Proteins are embedded within the phospholipid bilayer and serve various roles such as transport, signaling, and recognition.
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3. Why do scientists call the membrane a “mosaic”?
Answer: Because it is made up of many different types of molecules (like proteins, lipids, carbohydrates) arranged in a patchwork pattern.
> ✔ *Explanation:* The fluid mosaic model describes the membrane as a dynamic structure where proteins float in a sea of lipids—like tiles in a mosaic.
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4. On the image, label the:
a. Lipid bilayer → The double layer of phospholipids forming the main structure
b. Protein channel → A protein that spans the membrane with a pore (often shown as a tube-like structure)
c. Carbohydrate chains → Chains attached to the outer surface of the membrane (usually on glycoproteins or glycolipids)
> ✔ *Labeling Guide:*
- Lipid bilayer: The two layers of round circles (phospholipids)
- Protein channel: The large oval or tunnel-shaped structures going through the bilayer
- Carbohydrate chains: Branched structures extending outward from the top of the membrane
---
5. What three types of organisms have cell walls?
Answer: Plants, fungi, and bacteria
> ✔ *Explanation:* These organisms have rigid cell walls outside their cell membranes for structural support.
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6. What is the main function of the cell wall?
Answer: To provide structural support and protection to the cell.
> ✔ *Explanation:* The cell wall prevents the cell from bursting under osmotic pressure and maintains shape.
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7. What are plant cell walls composed of?
Answer: Cellulose
> ✔ *Explanation:* Plant cell walls are primarily made of cellulose, a strong polysaccharide that gives rigidity to plant cells.
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8. One of the most important functions of the cell membrane is to ____________ the movement of dissolved ____________ from the liquid on one side of the membrane to the liquid on the other.
Answer: Control / Regulate, substances (or molecules)
> ✔ *Explanation:* The membrane selectively allows certain molecules to pass through, maintaining balance inside the cell.
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9. A solution is a ___________________ of two or more substances.
Answer: Mixture
> ✔ *Explanation:* A solution consists of a solvent (like water) and solutes (dissolved substances).
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10. Define diffusion:
Answer: The movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached.
> ✔ *Explanation:* This passive process occurs due to random molecular motion.
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11. When the particles are the same throughout, the system has reached ________________
Answer: Equilibrium
> ✔ *Explanation:* At equilibrium, there is no net movement of particles because concentrations are equal.
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12. Diffusion depends on _________________ particle movements, therefore it [ does | does not ] require energy.
Answer: Random, does not
> ✔ *Explanation:* Diffusion is passive—it uses kinetic energy from molecules but doesn't require ATP.
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## OSMOSIS
13. If a substance is able to diffuse across a membrane, the membrane is said to be ___________________
Answer: Permeable (to that substance)
> ✔ *Explanation:* Permeability refers to the ability of a substance to pass through the membrane.
---
14. Define osmosis:
Answer: The diffusion of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
> ✔ *Explanation:* Osmosis specifically involves water movement due to concentration differences.
---
15. Isotonic means
Hypertonic means
Hypotonic means
Answers:
- Isotonic: Equal concentration of solutes on both sides of the membrane
- Hypertonic: Higher solute concentration outside the cell than inside
- Hypotonic: Lower solute concentration outside the cell than inside
> ✔ *Explanation:* These terms describe the relative solute concentrations between the cell and its environment.
---
16. Because cells are hypertonic in relation to fresh water, __________________ produces a net movement of water into the cell. If that happens, the cell will become __________________ and can even burst.
Answer: Osmosis, swollen (or turgid)
> ✔ *Explanation:* Freshwater is hypotonic to cells, so water moves in by osmosis. Animal cells may burst (lyse), but plant/bacteria cells don’t due to cell walls.
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17. In plant and bacteria cells, what keeps them from bursting due to osmotic pressure?
Answer: Cell wall
> ✔ *Explanation:* The rigid cell wall resists the inward pressure caused by water entering via osmosis.
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## FACILITATED DIFFUSION
18. Cell membranes have ________________________ that make it easy for certain molecules to cross the membrane.
Answer: Transport proteins (or carrier proteins)
> ✔ *Explanation:* These proteins help polar or large molecules move across the membrane without using energy.
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19. When proteins help molecules move across the membrane, it is called
Answer: Facilitated diffusion
> ✔ *Explanation:* This is a type of passive transport that uses proteins to speed up the movement of substances down their concentration gradient.
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✔ Final Summary:
This worksheet covers key concepts about:
- Structure and function of the cell membrane
- Diffusion and osmosis
- Tonicity (isotonic, hypertonic, hypotonic)
- Facilitated diffusion
- Role of cell walls in plants, fungi, and bacteria
All answers are based on standard biology curriculum content.
Let me know if you'd like this formatted as a printable PDF or need help labeling the diagram!
Parent Tip: Review the logic above to help your child master the concept of eighth grade science worksheet.
