Transport in Cells: A Summary

Transport of Molecules In and Out of Cells

• Cells require nutrients and oxygen to enter for respiration and chemical reactions.
• Waste products must exit to prevent interference with reactions and poisoning.
• Diffusion: Passive movement from high to low concentration; linked to kinetic energy.
• Osmosis: Passive diffusion of water from dilute to concentrated solution through a semi-permeable membrane.
• Active Transport: Movement requiring energy from low to high concentration.

Diffusion

• Diffusion occurs in liquids and gases due to free particle movement; doesn't occur in solids.
• It's passive, moving down a concentration gradient.
• Rate is influenced by concentration gradient; higher gradient equals higher rate.
• Diffusion relies on the kinetic energy of particles.

Examples in Living Organisms

• Gas Exchange: Oxygen diffuses into cells, carbon dioxide diffuses out.
• Glucose Exchange: Glucose diffuses into cells from blood.

Factors Affecting Rate of Diffusion:

• Size: Smaller molecules diffuse faster.
• Temperature: Higher temperature increases kinetic energy and diffusion rate.
• Concentration Gradient: Higher gradient increases rate.
• Distance: Shorter distance increases rate.
• Surface Area: Larger surface area increases rate.

Transport System in Multicellular Organisms

• Unicellular organisms rely on diffusion due to short distances and high surface area to volume ratio.
• Larger organisms need transport systems due to increased metabolic activity and small surface area to volume ratio.
• Transport systems carry substances by mass flow.
• They increase surface area for exchange (e.g., thin, flat leaves; alveoli in lungs).

Osmosis

• Water moves from high to low concentration through a semi-permeable membrane until equilibrium.
• Cell membranes are selectively permeable, allowing small molecules like water to pass.
• Dissolved substances attract water molecules, reducing free water concentration.
• Water flows from high-water potential (dilute) to low-water potential (concentrated) solutions.

Osmosis in Animal Cells

• Hypotonic Solution: Water enters the cell, causing it to burst (lysis).
• Hypertonic Solution: Water leaves the cell, causing it to shrivel.
• Isotonic Solution: No net water movement.

Osmosis in Plant Cells

• Hypotonic Solution: Water enters, cell becomes turgid, turgor pressure increases.
• Hypertonic Solution: Water exits, cell becomes flaccid (wilting), plasmolysis occurs.

Turgidity

• Essential for plant support and maximizing sun exposure.

Reverse Osmosis

• Removes salt from seawater by applying pressure to force water through a semi-permeable membrane.
• Requires energy.

Active Transport

• Moves particles against concentration gradient, requiring energy (ATP).
• Factors interfering with respiration (lack of oxygen/glucose, toxins) inhibit active transport.

Use in Living Cells

• Plant Root Hairs: Absorbing mineral ions from soil.
• Villi Cells: Absorbing simple sugars in the small intestine.

Surface Area to Volume Ratio (SA:V)

• Affects exchange of substances between organism and environment.
• High SA:V is efficient for exchange; low SA:V requires transport systems.
• Single-celled organisms have a high SA:V, facilitating diffusion.
• Larger organisms have a low SA:V, necessitating transport systems.
• Small organisms gain/lose heat faster due to high SA:V; large organisms gain/lose heat slower due to low SA:V.

Gaseous Exchange

• Breathing (ventilation): moving air in/out of the lungs.
• Gas exchange: transfer of gases from high to low concentration in alveoli (humans) or leaves (plants).
• Cellular respiration: releasing energy from glucose; may or may not require oxygen.

Characteristics of Efficient Gas Exchange Surface

1. Large surface area.
2. Thin epithelium.
3. High concentration gradient.
4. Rich blood supply.
5. Moist surface.

Structure of Flowering Plants - Angiosperms Leaf Internal Structure

• Waxy Cuticle: Reduces water loss, prevents microbe entry.
• Upper Epidermis: Transparent, allows light to pass.
• Mesophyll:
  • Palisade Layer: Long, chloroplast-rich cells for photosynthesis.
  • Spongy Layer: Loosely packed cells with air spaces for gas exchange.
• Veins: Transport water/minerals (xylem) and food (phloem).
• Lower Epidermis: Contains stomata for gas exchange.

Gaseous Exchange in Humans

• Aerobic respiration requires oxygen, produces carbon dioxide.
• Lungs provide large, moist surface area for gas exchange.

Human Respiratory System:

• Nose/Nasal Cavity: Filters and warms air.
• Trachea: Supported by cartilage rings.
• Bronchi: Two tubes branching from trachea.
• Bronchioles: Smaller branches from bronchi.
• Alveoli: Air-filled sacs at the end of bronchioles; site of gas exchange.

Ventilation

• Inhalation: Diaphragm contracts, ribs move up and out, increasing lung volume and decreasing pressure.
• Exhalation: Diaphragm relaxes, ribs move down and in, decreasing lung volume and increasing pressure.

Differences in Inspired vs Expired air:

• Inspired: High O2, Low CO2, N2 unchanged
• Expired: Low O2, High CO2, N2 unchanged.

Lung Capacity and Breathing Rate

• Breathing rate increases during exercise.
• Fit person has lower heart rate and faster recovery time.

Negative Impact of Smoking on Human Health

• Tar: Prevents cilia movement, damages alveoli, contains carcinogens.
• Nicotine: Addictive, increases heart rate and blood pressure.
• Carbon Monoxide: Reduces oxygen carrying capacity.
• Emphysema: Damages alveoli -> shortness of breath.
• Coronary Heart Disease