Cell Biology and Transport Study Notes

Characteristics of Eukaryotic and Prokaryotic Cells

  • Eukaryotic Cells

    • Organisms such as animals and plants are classified as eukaryotic.

    • These cells contain genetic material (DNA\text{DNA}) that forms chromosomes.

    • ned nucleus.The genetic material is enclosed within a defi

  • Prokaryotic Cells (Bacteria)

    • Bacteria are single-celled organisms.

    • They lack a nucleus; instead, their genetic material consists of a single loop of DNA\text{DNA}.

    • They contain small, additional rings of DNA\text{DNA} known as plasmids. Bacteria may possess more than one of these.

    • Prokaryotic cells are significantly smaller in size compared to eukaryotic cells.

    • Structural components include:

      • Cell wall

      • Cytoplasm

      • Cell membrane

      • Plasmid DNA\text{DNA} rings

      • Bacterial DNA\text{DNA} loop (free-floating, no nucleus)

      • Flagellum (used for movement)

Cell Structures and Their Functions

  • Nucleus: Contains the cell's DNA\text{DNA} and controls activities.

  • Cytoplasm: A jelly-like substance where the majority of chemical reactions occur within the cell.

  • Cell Membrane: Regulates the movement of substances entering and exiting the cell.

  • Mitochondria: The site where energy is released through the process of aerobic respiration.

  • Ribosomes: The specific site responsible for protein synthesis (enabling the production of proteins).

  • Cell Wall: Composed of cellulose in plants, providing strength and structural support to the cell.

  • Permanent Vacuole: Found in plant cells; contains cell sap.

  • Chloroplasts: Found in plant cells; contain the green pigment chlorophyll, which absorbs light energy required for photosynthesis.

Cell Differentiation and Specialised Cells

  • Cell Differentiation

    • In animals, most cells differentiate at an early stage of development.

    • In plants, cells retain the ability to differentiate throughout the entirety of the organism's lifetime.

  • Sperm Cell

    • Function: To fertilise an ovum (egg).

    • Adaptations:

      • Possesses a tail to enable swimming toward the ovum for fertilisation.

      • Contains a high density of mitochondria to release the energy necessary for the sperm to swim.

  • Red Blood Cell

    • Function: To transport oxygen throughout the body.

    • Adaptations:

      • Lacks a nucleus to provide more internal space for carrying oxygen molecules.

      • Contains haemoglobin, a red pigment that binds to oxygen.

      • Features a flat bi-concave disc shape, which increases the surface area-to-volume ratio for efficient gas exchange.

  • Muscle Cell

    • Function: To contract and relax, facilitating movement.

    • Adaptations:

      • Contains specialised protein fibres that can contract to shorten the length of the cell.

      • Contains numerous mitochondria to provide the energy required for muscle contraction.

  • Nerve Cell (Neurone)

    • Function: To carry electrical impulses across different parts of the body.

    • Adaptations:

      • Features branched endings called dendrites to establish connections with other neurones or effectors.

      • The axon is insulated by a myelin sheath, which increases the transmission speed of electrical impulses.

  • Root Hair Cell

    • Function: To absorb mineral ions and water from the soil.

    • Adaptations:

      • Features a long projection that increases the surface area of the cell, speeding up the absorption process.

      • Contains many mitochondria to release energy needed for the active transport of mineral ions from the soil.

  • Palisade Cell

    • Function: To enable photosynthesis within the leaf.

    • Adaptations:

      • Packed with many chloroplasts containing chlorophyll to maximize light energy absorption.

      • Positioned at the top surface of the leaf to receive the maximum amount of sunlight.

Microscopy

  • Comparing Microscope Types

    • Light Microscope:

      • Uses light to form images.

      • Can be used to view living samples.

      • Relatively inexpensive.

      • Offers low magnification and low resolution.

    • Electron Microscope:

      • Uses a beam of electrons to form images.

      • Samples cannot be living.

      • Expensive equipment.

      • Offers high magnification and high resolution, allowing for the visualization of sub-cellular structures like ribosomes.

  • Magnification Calculation:     magnification=image sizeactual size\text{magnification} = \frac{\text{image size}}{\text{actual size}}

Transport Processes: Diffusion, Osmosis, and Active Transport

  • Diffusion

    • Definition: The spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration.

    • Energy: A passive process; requires no energy.

    • Movement: Particles move down the concentration gradient.

    • Factors Affecting Rate: Difference in concentration (gradient), temperature, and the surface area of the membrane.

    • Examples:

      • Humans: Nutrients in the small intestine diffuse into capillaries via villi; Oxygen diffuses from alveoli into capillary blood; Carbon dioxide diffuses from capillary blood into alveoli; Urea diffuses from cells into the blood for excretion.

      • Fish: Oxygen from water diffuses into blood in gill filaments; Carbon dioxide diffuses from blood into the water.

      • Plants: Carbon dioxide diffuses into leaves via stomata; Oxygen diffuses out of leaves via stomata.

  • Osmosis

    • Definition: The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

    • Energy: A passive process; requires no energy.

    • Movement: Water moves from an area of lower solute concentration to an area of higher solute concentration.

    • Example: Water moves from the soil into a root hair cell.

  • Active Transport

    • Definition: The movement of particles from a more dilute solution to a more concentrated solution using energy from respiration.

    • Energy: Requires energy released by respiration.

    • Movement: Particles move against the concentration gradient (from low to high concentration).

    • Examples:

      • Humans: Absorption of sugar molecules from the small intestine into the blood, even when the concentration in the blood is higher.

      • Plants: Absorption of mineral ions into root hair cells from dilute soil solutions.

Adaptations for Exchange

  • Villi (Small Intestine): Long and thin (increases surface area), one-cell-thick membrane (short diffusion pathway), and good blood supply (maintains a steep concentration gradient).

  • Lungs (Alveoli): Huge surface area, moist membranes (increases diffusion rate), one-cell-thick membranes, and excellent blood supply to maintain the concentration gradient.

  • Fish Gills: Large surface area provided by gill filaments, thin layer of cells (short pathway), and good blood supply.

Retrieval Questions & Discussion

  • Q1: What are two types of eukaryotic cell?

    • A: Animal and plant cells.

  • Q2: What type of cell are bacteria?

    • A: Prokaryotic cells.

  • Q3: Where is DNA found in animal and plant cells?

    • A: In the nucleus.

  • Q4: What is the function of the cell membrane?

    • A: It controls the movement of substances in and out of the cell.

  • Q5: What is the function of mitochondria?

    • A: It is the site of respiration to transfer energy for the cell.

  • Q6: What is the function of chloroplasts?

    • A: They contain chlorophyll to absorb light energy for photosynthesis.

  • Q7: What is the function of ribosomes?

    • A: They enable the production of proteins (protein synthesis).

  • Q8: What is the function of the cell wall?

    • A: It strengthens and supports the cell.

  • Q9: What is the structure of the main genetic material in a prokaryotic cell?

    • A: A single loop of DNA\text{DNA}.

  • Q10: How are electron microscopes different to light microscopes?

    • A: Electron microscopes use beams of electrons instead of light, cannot view living samples, are much more expensive, and provide much higher magnification and resolution.

  • Q11: What is the function of a red blood cell?

    • A: It carries oxygen around the body.

  • Q12: Give three adaptations of a red blood cell.

    • A: No nucleus, contains haemoglobin, and has a bi-concave disc shape.

  • Q13: What is the function of a nerve cell?

    • A: It carries electrical impulses around the body.

  • Q14: Give two adaptations of a nerve cell.

    • A: Branched endings and a myelin sheath to insulate the axon.

  • Q15: What is the function of a sperm cell?

    • A: To fertilise an ovum (egg).

  • Q16: Give two adaptations of a sperm cell.

    • A: A tail and a high number of mitochondria.

  • Q17: What is the function of a palisade cell?

    • A: It carries out photosynthesis in a leaf.

  • Q18: Give two adaptations of a palisade cell.

    • A: Lots of chloroplasts and located at the top surface of the leaf.

  • Q19: What is the function of a root hair cell?

    • A: It absorbs minerals and water from the soil.

  • Q20: Give two adaptations of a root hair cell.

    • A: A long projection and many mitochondria.

  • Q21: What is diffusion?

    • A: The net movement of particles from an area of high concentration to an area of low concentration along a concentration gradient; this is a passive process that does not require energy from respiration.

  • Q22: Name three factors that affect the rate of diffusion.

    • A: Concentration gradient, temperature, and membrane surface area.

  • Q23: How are villi adapted for exchanging substances?

    • A: They are long and thin (increasing surface area), have a one-cell-thick membrane (short diffusion pathway), and a good blood supply (maintaining the concentration gradient).

  • Q24: How are the lungs adapted for efficient gas exchange?

    • A: Alveoli provide a large surface area, membranes are moist (increasing diffusion rate), membranes are one-cell-thick (short pathway), and they have a good blood supply.

  • Q25: How are fish gills adapted for efficient gas exchange?

    • A: Large surface area for gas diffusion, thin layer of cells for a short pathway, and a good blood supply.

  • Q26: What is osmosis?

    • A: The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

  • Q27: Give one example of osmosis in a plant.

    • A: Water moving from the soil into the root hair cell.

  • Q28: What is active transport?

    • A: The movement of particles against a concentration gradient—from a dilute solution to a more concentrated solution—using energy from respiration.

  • Q29: Why is active transport needed in plant roots?

    • A: Because the concentration of mineral ions in the soil is lower than inside the root hair cells; ions must move against the gradient.

  • Q30: What is the purpose of active transport in the small intestine?

    • A: To allow sugars to be absorbed when the concentration of sugar in the small intestine is lower than the concentration in the blood.