Biology Osmosis and Science Skills (copy)

osmosis

The passive movement of water from a low solute concentration to a high solute concentration through a selectively permeable membrane.

diffusion

The passive movement of molecules from an area of high concentration to an area of low concentration.

tonicity

Tonicity describes the relative concentration of solutes in two solutions separated by a semipermeable membrane.

hypertonic solution

A solution with a higher solute concentration compared to another, causing water to move into it.

hypotonic solution

A solution with a lower solute concentration compared to another, causing water to move out of it.

isotonic solution

A solution with equal solute concentration compared to another, resulting in no net water movement.

plant cells in a hypotonic solution

They swell and become turgid due to water intake.

animal cells in a hypotonic solution

They may swell and burst (lyse).

cells in a hypertonic solution

Water leaves the cells, causing them to shrink.

molecule that can freely diffuse

Oxygen (O₂) or carbon dioxide (CO₂).

ions and membrane diffusion

Because they are charged and cannot pass through the nonpolar lipid bilayer.

factors affecting the rate of diffusion

Temperature, concentration gradient, surface area, molecule size, and polarity.

aquaporins

Protein channels that facilitate faster water movement across the membrane.

percentage change in mass formula

% Change = (Final Mass - Initial Mass) / Initial Mass × 100

type of transport for osmosis and diffusion

Passive transport - they do not require energy.

What is the purpose of developing aims and questions in a biology investigation?

To guide the direction of the investigation and focus data collection.

What are independent, dependent and controlled variables?

Independent: the variable changed; Dependent: the variable measured; Controlled: variables kept constant.

What is a hypothesis?

A testable prediction that explains what might happen in an experiment.

Why are hypotheses important?

They provide a focus for the investigation and allow predictions to be tested.

What is a controlled experiment?

An experiment in which only one variable is changed at a time to test its effect.

What are examples of investigation methodologies?

Case study, classification and identification, controlled experiment, correlational study, fieldwork, literature review, modelling, simulation, product/system development.

Why is it important to select appropriate equipment and procedures in an investigation?

To ensure valid, accurate and reliable data are collected and sources of error are minimised.

What is the difference between qualitative and quantitative data?

Qualitative data is descriptive; quantitative data is numerical.

What must be considered when designing sampling techniques?

Sample size, representation, potential bias, and sources of error or uncertainty.

Why is collaboration important in scientific investigations?

It allows for more perspectives, verification, and division of tasks within constraints.

What is the purpose of a risk assessment in scientific investigations?

To identify and minimise potential safety hazards using SDS and lab safety guidelines.

How is primary data different from secondary data?

Primary data is generated by the researcher; secondary data is obtained from existing sources.

What are accuracy and precision?

Accuracy: closeness to the true value; Precision: consistency of repeated results.

What are repeatability and reproducibility?

Repeatability: consistent results within the same lab; Reproducibility: consistent results across different labs.

What are random and systematic errors?

Random: unpredictable variation; Systematic: consistent bias in measurement.

How do you identify outliers?

Data points that deviate significantly from the rest of the data set.

Why should experiments be repeated?

To improve the reliability and robustness of results.

How can investigations be improved?

By refining methods, controlling variables more effectively, and reducing sources of error or bias.

What is an evidence-based conclusion?

A conclusion that is directly supported by experimental data and not opinion.

How do you evaluate if evidence supports a hypothesis?

Compare results to the predicted outcomes stated in the hypothesis.

What are the limitations of scientific conclusions?

Limited data, uncontrolled variables, sample size, or measurement uncertainty.

What is the role of scientific reasoning in conclusions?

To justify findings logically based on the data and context.

Why is it important to distinguish opinion from evidence?

To ensure conclusions are scientifically valid and not biased or anecdotal.

What are the key differences between prokaryotic and eukaryotic cells?

Prokaryotic cells (e.g., bacteria): no membrane-bound organelles, circular DNA, small size (1–10 µm). Eukaryotic cells (e.g., plant/animal): membrane-bound organelles, linear chromosomes, larger (10–100 µm). (2A)

Why is surface area-to-volume ratio (SA :V) critical in cells?

It determines how efficiently materials are exchanged. Smaller cells with a high SA :V ratio can exchange nutrients and waste more rapidly than larger ones. 2C

How do organelles improve efficiency in eukaryotic cells?

By compartmentalising functions (e.g., protein synthesis in ribosomes, energy in mitochondria), organelles localise processes and reduce conflict between reactions.2B

Describe the structure and function of the plasma membrane.

Composed of a phospholipid bilayer with embedded proteins, it regulates what enters/leaves the cell via passive (diffusion, osmosis) and active transport. 3A

What is facilitated diffusion and how does it differ from active transport?

Facilitated diffusion uses channel proteins to move molecules down their concentration gradient. Active transport requires energy (ATP) to move molecules against the gradient.3B

Define osmosis and explain its role in cells.

Osmosis is the diffusion of water across a semipermeable membrane from low solute concentration to high solute concentration, balancing cell water content.3C

What structures are unique to plant cells?

Chloroplasts (photosynthesis), cell wall (rigid support), large central vacuole (storage and pressure maintenance). 2B

What is the function of mitochondria?

They are the site of aerobic respiration, converting glucose and oxygen into ATP, the cell's usable energy. 2B

Why are membranes described as "fluid mosaic"?

The plasma membrane is "fluid" because phospholipids move freely, and "mosaic" due to embedded proteins varying in shape and function. 3A

How do hydrophilic and hydrophobic regions affect membrane function?

Hydrophilic heads face outward (water-loving), hydrophobic tails face inward (repel water), forming a selective barrier. 3A

What limits the maximum size of a cell?

Diffusion becomes inefficient as volume increases faster than surface area, limiting nutrient exchange and waste removal. 2C

Give examples of organelles and their specialised roles.

Ribosomes: protein synthesis Golgi apparatus: packaging proteins Lysosomes: digesting cell waste 2B

How do cells adapt shape to maintain high SA :V?

Cells may be long and thin (e.g., nerve cells) or have microvilli to increase surface area. 2C

How does the structure of the membrane enable selective permeability?

The hydrophobic interior blocks polar molecules unless assisted by proteins; small nonpolar molecules diffuse freely. 3B

What is the role of channel and carrier proteins?

Channel proteins form pores for specific ions. Carrier proteins change shape to move molecules. Both facilitate transport across the membrane. 3B

What is the difference between accuracy and precision?

Accuracy: Closeness to the true value. Precision: Consistency of repeated measurements. (Chapter 1, Key Skill: Investigation Design)

What are the key components of a scientific report?

Title, Aim, Hypothesis, Method, Results, Discussion, Conclusion, References. (Chapter 1, Science Communication)

What is the difference between primary and secondary data?

Primary: Collected firsthand (experiments, surveys). Secondary: Sourced from others (journals, databases). (Chapter 1, Scientific Evidence)

What is a controlled experiment?

An experiment where only one variable is changed (independent variable) while others are kept constant. (Chapter 1, Investigation Design)

What is validity in an experiment?

Whether the experiment tests what it claims to test (appropriate method, controls, measurements). (Chapter 1, Investigation Design)

What is reproducibility?

The ability of an experiment to be repeated by others with similar results. (Chapter 1, Investigation Design)

What is a hypothesis?

A testable prediction based on prior knowledge. (Chapter 1, Scientific Evidence)

What is the difference between qualitative and quantitative data?

Qualitative: Descriptive (e.g., color, texture). Quantitative: Numerical (e.g., pH, temperature). (Chapter 1, Investigation Design)

What are sources of error in experiments?

Random errors (unpredictable variations). Systematic errors (flaws in method/equipment). (Chapter 1, Scientific Evidence)

What is bias in scientific research?

Prejudice that skews results (e.g., selective reporting). (Chapter 1, Scientific Evidence)

What is the difference between anecdote and evidence?

Anecdote: Personal story (not reliable). Evidence: Data-supported findings. (Chapter 1, Scientific Evidence)

What are prokaryotic cells?

No nucleus, no membrane-bound organelles, smaller (1-5µm). Example: Bacteria. (Chapter 2A)

What is the function of ribosomes?

Protein synthesis (found in both prokaryotes & eukaryotes). (Chapter 2B)

What is the nucleus?

Control center, contains DNA.(Chapter 2B)

Why is SA :V important for cells?

As cells grow, volume increases faster than SA, limiting nutrient exchange. Small cells = efficient diffusion. (Chapter 2C)

How do cells overcome SA :V limitations?

Folding membranes (e.g., microvilli, cristae in mitochondria). (Chapter 2C)

What is the function of mitochondria?

ATP production (cellular respiration). (Chapter 2B)

What is the function of chloroplasts?

Photosynthesis (plant cells only). (Chapter 2B)

What is the endoplasmic reticulum (ER)?

Rough ER: Protein synthesis (has ribosomes). Smooth ER: Lipid synthesis/detoxification. (Chapter 2B)

What is the Golgi apparatus?

Modifies, sorts, packages proteins for secretion. (Chapter 2B)

What is the fluid mosaic model?

Describes the plasma membrane as a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates. Fluid = molecules can move; Mosaic = protein pattern. (Chapter 3A)

What is the role of cholesterol in the membrane?

Stabilizes membrane fluidity (prevents solidification at low temps & excessive fluidity at high temps). (Chapter 3A)

What are integral vs. peripheral proteins?

Integral: Embedded in membrane (e.g., channel proteins). Peripheral: Attached to surface (e.g., receptor proteins). (Chapter 3A)

What is simple diffusion?

Movement of small, nonpolar molecules (e.g., O₂, CO₂) down their concentration gradient (no energy). (Chapter 3B)

What is osmosis?

Diffusion of water across a semipermeable membrane (high → low water concentration). (Chapter 3B)

What happens to a cell in a hypertonic solution?

Water leaves cell → cell shrinks (crenation in animals, plasmolysis in plants). (Chapter 3B)

What is facilitated diffusion?

Passive transport of polar/large molecules via protein channels/carriers (e.g., glucose). (Chapter 3B)

What is active transport?

Movement of substances against their gradient (low → high) using ATP (e.g., Na⁺/K⁺ pump). (Chapter 3C)

What is the sodium-potassium pump?

3 Na⁺ out, 2 K⁺ in per ATP → maintains resting membrane potential in neurons. (Chapter 3C)

What is bulk transport?

Endocytosis (into cell) vs. exocytosis (out of cell). Example: Phagocytosis (cell "eating"). (Chapter 3C)

How do prokaryotes replicate?

Binary fission: DNA replicates → cell splits. (Chapter 4A)

What are the phases of the cell cycle?

Interphase (G₁, S, G₂) → Mitosis (PMAT) → Cytokinesis. (Chapter 4B)

What is metaphase?

Chromosomes align at the equator (metaphase plate). (Chapter 4B)

How does cytokinesis differ in plants vs. animals?

Animals: Cleavage furrow. Plants: Cell plate forms. (Chapter 4B)

What is apoptosis?

Programmed cell death (removes damaged cells; no inflammation). (Chapter 4C)

How does cancer disrupt the cell cycle?

Uncontrolled mitosis due to mutations (e.g., in p53 tumor suppressor gene). (Chapter 4C)

What are characteristics of cancer cells?

Rapid division, ignore apoptosis, metastasize, abnormal nuclei. (Chapter 4C)

What are totipotent stem cells?

Can become any cell type (including placenta; e.g., zygote). (Chapter 4D)

What are pluripotent stem cells?

Can become any body cell (e.g., embryonic stem cells). (Chapter 4D)

What is transpiration?

Water loss from leaves via stomata (driven by evaporation). (Chapter 5A)

What is the cohesion-tension theory?

Water molecules stick together (cohesion) and are pulled up xylem by evaporation (transpiration pull). (Chapter 5B)

What is the role of root hairs?

Increase SA for water/mineral absorption. (Chapter 5B)

What are the 3 main digestive enzymes?

Amylase (carbs), protease (proteins), lipase (lipids). (Chapter 5C)

What is villi’s role in the small intestine?

Increase SA for nutrient absorption (contain capillaries + lacteals). (Chapter 5C)

What does the liver do in digestion?

Produces bile (emulsifies fats), stores glycogen, detoxifies blood. (Chapter 5C)

What is the nephron’s function?

Filters blood → urine via glomerulus (filtration), tubules (reabsorption/secretion). (Chapter 5E)

What is negative feedback?

Reverses a change (e.g., insulin lowers high blood glucose). (Chapter 6B, 6C, 6D)