Biology Unit 1 Exam Revision

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Why do cells have a maximum size limit?

Primarily due to their Surface area to Volume ratio. Because as cells grow, their volume increases faster than their surface area, making it harder to exchange nutrients and waste across the membrane.

How does compartmentalization help eukaryotic cells with size limitations?

It enables eukaryotic cells to manage their size and complex functions more effectively.

List three differences between animal and plant cells.

1. Plant cells have a cell wall; animal cells do not. 2. Plant cells have chloroplasts; animal cells do not. 3. Plant cells have a large central vacuole; animal cells have small vacuoles.

How do prokaryotic and eukaryotic cells differ in terms of genetic material and organelles?

Prokaryotes lack a nucleus and membrane-bound organelles; eukaryotes have both.

What is the function of the Golgi apparatus?

It modifies, sorts, and packages proteins and lipids for secretion.

Name two organelles unique to plant cells and their roles.

Chloroplasts (photosynthesis) and central vacuole (storage/turgor pressure).

Describe the structure and function of the rough endoplasmic reticulum.

It consists of folded membranes with ribosomes and synthesizes and transports proteins.

How do lysosomes contribute to intracellular digestion?

They contain digestive enzymes to break down waste and pathogens.

What is the structure of the plasma membrane?

It is a phospholipid bilayer with hydrophilic heads facing outward and hydrophobic tails inward.

What roles do cholesterol and proteins play in the plasma membrane?

Cholesterol maintains fluidity, while proteins act as channels and receptors.

How does the plasma membrane maintain selective permeability?

It allows small/nonpolar molecules to pass while blocking large/polar ones.

Compare diffusion, facilitated diffusion, and active transport.

Diffusion is passive and requires no energy for small/nonpolar molecules; facilitated diffusion is passive but uses channel proteins; active transport requires ATP to move molecules against the gradient.

How do endocytosis and exocytosis differ?

Endocytosis involves the cell engulfing material (e.g., phagocytosis of bacteria), while exocytosis expels material (e.g., neurotransmitter release).

What happens to a red blood cell in a hypertonic solution?

The cell shrinks (crenation) due to water loss.

How do plant cells respond to hypotonic solutions compared to animal cells?

Plant cells become turgid (vacuole swells), while animal cells may lyse.

Why does active transport require ATP while diffusion does not?

Active transport moves molecules against their concentration gradient, requiring energy, while diffusion relies on the gradient and does not need energy.

How does a concentration gradient drive passive transport?

Passive transport occurs as molecules move from an area of higher concentration to an area of lower concentration.

Draw and label a mitochondrion. How does its structure support ATP production?

Mitochondria have a double membrane with cristae (folds) that increase surface area for ATP production.

What is the role of thylakoids in chloroplasts?

Thylakoids contain chlorophyll and are the site of light-dependent reactions in photosynthesis.

Why is photosynthesis essential for life on Earth?

It fixes CO₂ into glucose (food) and releases O₂, sustaining life.

Write the balanced chemical equation for photosynthesis.

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

How are chloroplasts adapted for efficient photosynthesis?

Thylakoids provide a large surface area for light absorption, and stroma contains enzymes for the Calvin cycle.

How does CO₂ enter a leaf and what happens to the glucose produced?

CO₂ enters via stomata; glucose is transported as sucrose via phloem.

Compare aerobic and anaerobic respiration.

Aerobic respiration produces 36-38 ATP (efficient), while anaerobic respiration produces only 2 ATP (e.g., lactic acid fermentation).

Write the word equation for aerobic respiration.

Glucose + oxygen → carbon dioxide + water + ATP.

How do chemosynthetic autotrophs differ from photosynthetic ones?

Chemosynthetic autotrophs derive energy from chemical reactions, while photosynthetic autotrophs use sunlight.

What are the steps of binary fission in prokaryotes?

1. DNA replicates. 2. Cell elongates and DNA moves to poles. 3. Cell splits (cytokinesis).

What happens during metaphase in animal cells?

Chromosomes align at the equator of the cell.

How does cytokinesis differ in plants vs. animals?

In plants, a cell plate forms; in animals, a cleavage furrow forms.

Describe what occurs during G1, S, and G2 phases of interphase.

G1: Growth. S: DNA replication. G2: Prepares for mitosis.

Why is apoptosis important in development and disease prevention?

It removes damaged cells and prevents cancer.

Where are the checkpoints in the cell cycle, and what do they monitor?

G1 checkpoint checks for DNA damage; M checkpoint ensures chromosomes are attached to the spindle.

How can faulty apoptosis lead to cancer?

Faulty apoptosis can result in uncontrolled cell division, leading to cancer.

What are three characteristics of cancer cells?

Uncontrolled growth, evasion of apoptosis & immune system evasion

What is the difference between totipotent and pluripotent stem cells?

Totipotent stem cells can become any cell type, while pluripotent stem cells can become most cell types.

How does a stem cell become a specialized neuron?

Stem cells receive signals to express specific genes, leading to specialization.

Arrange these in order: organ, tissue, organism, cell, organ system.

Cell → Tissue → Organ → Organ System → Organism.

How does xylem structure support water transport?

Xylem consists of dead, hollow cells (tracheids/vessels) that transport water and have lignin to strengthen walls.

What waste products are removed by the kidneys?

Urea, excess ions, and excess water.

Where does filtration occur in a nephron?

Filtration occurs in the glomerulus and is collected in Bowman's capsule.

How is water reabsorbed in the nephron?

Water is reabsorbed in the proximal tubule along with glucose and ions.

How do stomata regulate water loss in plants?

Stomata open for CO₂ during the day and close at night to conserve water.

Describe how the body regulates blood glucose levels.

Insulin lowers glucose levels by storing it as glycogen, while glucagon raises glucose levels by breaking down glycogen.

How does Type 1 diabetes disrupt homeostasis?

It involves autoimmune destruction of insulin-producing beta cells, leading to high blood glucose levels.

Give an example of a negative feedback loop in humans.

Thermoregulation: Sweating cools the body if temperature rises.

Write a hypothesis for an experiment testing enzyme activity at different pH levels.

If pH increases, enzyme activity will decrease because the active site denatures.

Why is a control group important in experiments?

It provides a baseline to compare experimental results.

Scenario:
A botanist wants to investigate how light intensity affects the growth of sunflower seedlings. They set up an experiment using three groups of sunflowers:

• Group A: Placed under a bright grow light (1000 lux) for 12 hours/day.

• Group B: Placed under a dim grow light (500 lux) for 12 hours/day.

• Group C: Placed in complete darkness (0 lux).

All groups are given the same amount of water daily, planted in identical pots with the same soil mix, and kept at a constant temperature of 22°C. After 4 weeks, the botanist measures the height (in cm) of each plant.

Independent: Light intensity. Dependent: Plant height. Control: Same soil, water, temperature.

What ethical concerns arise from human stem cell research?

Debate over the use of embryonic stem cells, which involves the destruction of embryos.

What makes a bioethical argument balanced and credible?

It weighs scientific benefits against moral concerns, such as animal rights.

How might utilitarianism justify animal testing in medical research?

It may be justified if the benefits, such as curing diseases, outweigh the harm to animals.