L2 Unit 1 AOS2 Bio: Plant and Animal Cell Specialisation

Cells to Systems

• Multicellular life requires cells to function together, providing energy, nutrients, oxygen, and removing waste to maintain equilibrium and stable internal conditions.
• Cells can become specialized to perform specific individual functions, and as they increase in size and complexity, greater cooperation and coordination are required to survive.

Organisation of Plants

• Vascular plants require vascular tissue to transport water and nutrients throughout the plant.
• Plant tissues include:
  • Dermal tissue: a single layer of cells that covers the outside of a plant, secreting a film to form a physical barrier, reducing water loss and physical damage.
  • Ground tissue: makes up the majority of the interior of the plant, carrying out metabolic functions, and vascular tissues run through it, carrying water and nutrients.
• Plant organs include:
  • Reproductive organs: flowers, fruits, and seeds.
  • Non-reproductive organs: leaves, stems, and roots.
• Plant systems include:
  • Root system: located underground, absorbs water and nutrients from the soil, providing support and structure.
  • Shoot system: includes reproductive organs, stems, and leaves, responsible for photosynthesis and growth.

Organisation of Animals

• Animal cells combine to form four major tissue types:
  • Muscle tissue: enables movement by generating force.
  • Nervous tissue: detects stimuli and transmits electrical signals.
  • Connective tissue: provides structural support and connects organs.
  • Epithelial tissue: forms barriers, provides protection, and assists in secretion and absorption.
• Animal organs include:
  • Tissues + cells that perform a specific function.
  • Examples: heart, lungs, liver, kidneys, etc.
• Animal systems include:
  • Circulatory system: pumps blood throughout the body, providing oxygen and nutrients.
  • Respiratory system: brings oxygen into the body and removes carbon dioxide.
  • Nervous system: controls and coordinates body functions.
  • Digestive system: breaks down and absorbs nutrients.

Plant Vascular Tissues

• Vascular tissues transport water and nutrients throughout the plant.
• Includes xylem and phloem tissue.
  • Xylem tissue: transports water and minerals from the roots to the leaves in one direction.
  • Phloem tissue: transports sugars and other nutrients around the plant in both directions.

Mechanisms of Water and Nutrient Movement in Vascular Plants

• Water and essential nutrients are absorbed from the soil by the roots.
• Water and nutrients travel up the xylem to the leaves.
• Photosynthesis occurs, requiring water to produce glucose.
• Glucose and other nutrients are transported throughout the rest of the plant in the phloem.

Root System

• Functions:
  • Provide stability and support to a plant.
  • Absorb water and minerals from the soil.
• Root cells:
  • Absorb water and nutrients from the soil.
  • Root hair cells are finger-like projections that increase the surface area of the roots.

Pathways of Water and Nutrient Absorption into Roots

• Extracellular pathway: water and dissolved solutes diffuse into the roots through the apoplastic route.
• Cytoplasmic pathway: minerals passively diffuse into the cytoplasm or are taken up via active transport in root hair cells.

Structure and Function of the Xylem

• Long, skinny tubes that run throughout the plant, made up of vessel elements and tracheids.
• Vessel elements are larger and stack end-to-end, forming a tube that lets water flow vertically through the xylem.
• Tracheids are smaller and have tapered ends, allowing water to flow horizontally through pits before continuing vertically.

Similarities and Differences between Vessel Elements and Tracheids

• Both are hollow cells that strengthen the cell wall with lignin deposits.
• Vessel elements are larger and stack end-to-end, while tracheids are smaller and have overlapping endings.

Sieve Cells and Companion Cells

• Regulate the entry of nutrients into the phloem.
• Companion cells are located next to sieve cells and help regulate the entry of nutrients.

Movement in the Xylem

• Transpiration: the evaporation of water from leaves and the movement of liquids up the xylem.
• Water evaporates from the leaf and exits through the stomata, creating a force that draws water up from the xylem to the leaf.
• Capillary action helps water flow into the xylem.

Transpiration

• Important for regulating heat and water balance, distributing nutrients, and preventing wilting.
• Characteristics:
  • Water evaporates from the leaf and exits through the stomata.
  • Air pressure in the leaf becomes lower than the pressure in the roots.
  • A force that draws water up from the xylem to the leaf is generated.### Adhesion and Cohesion
• Adhesion is the attraction between a liquid and a surface, causing the liquid to flow in narrow tubes.
• Examples of adhesion: water flowing in narrow tubes, sticking of bandaids to the skin.

Translocation

• Translocation is the movement of substances from a source to other tissues in the plant via the phloem.
• Sources: tissues or plants where substances are produced or enter the plant.
• Sinks: tissues of a plant where substances are stored.
• Glucose is the main nutrient of plants.

Steps of Translocation

• Glucose is produced in the leaf cell and pumped into the companion cells.
• Glucose diffuses into the sieve cells of the phloem, increasing the concentration of glucose.
• Water diffuses into the sieve cells from the xylem, increasing turgor pressure.
• The liquid in the phloem gets pushed throughout the plant, and glucose is actively transported into required cells (sinks).
• Glucose is unloaded into sink cells, decreasing the concentration of glucose in the phloem.

Turgor Pressure

• Turgor pressure is the internal pressure of a plant cell against its cell wall.
• High turgor pressure makes the cell stiff and rigid.
• Low turgor pressure makes the cell flimsy and less supportive.

Factors Affecting Transpiration Rates

• Temperature: high temperatures increase transpiration rates.
• Light: necessary for photosynthesis and allows for gas exchange.
• Humidity: low humidity increases transpiration rates.
• Water availability: affects transpiration rates.

Guard Cells

• Guard cells are a pair of curved cells that surround a stoma.
• When stomata are closed, gases cannot freely exchange in the leaf, reducing photosynthesis, transpiration, and water loss.
• Increasing transpiration rates: pump K+ ions into guard cells, increasing solute concentration, and water diffuses into guard cells via osmosis.
• Decreasing transpiration rates: pump K+ ions out of guard cells, and water diffuses out of guard cells, making them flaccid.