Biology practise test

Autotrophs and Heterotrophs

• Autotrophs: obtain glucose through self-manufacture (photosynthesis)
  • Use energy from the sun to convert water and carbon dioxide into glucose
  • Glucose gives plants energy and is used to make cellulose for growth and cell walls
• Heterotrophs: obtain organic nutrients by consuming autotrophs or other heterotrophs
  • Rely on autotrophs and other organisms for nutrition
  • Examples: most bacterial heterotrophs, which rely on dissolved organic material for carbon, nitrogen, and phosphorus requirements

Plant Structures

• Roots:
  • Anchor the plant, transport water, minerals, and sugars, and store excess nutrients
  • Function similar to our feet, helping the plant balance
• Stem:
  • Functions in support, conduction, photosynthesis, and storage
• Leaves:
  • Organs of the shoot system adapted for photosynthesis
  • Contain chloroplasts and stomata for gas exchange

Gas Exchange

• Plants:
  • Exchange gases through stomata (tiny pores) on the underside of leaves
  • Guard cells regulate stomatal opening and closing
• Animals:
  • Exchange gases through specialized respiratory organs (e.g., lungs, gills, skin)
  • Cells in both plants and animals perform respiration

Unicellular and Multicellular Organisms

• Unicellular organisms:
  • Consist of one cell only
  • Examples: Amoeba, Paramecium
• Multicellular organisms:
  • Consist of multiple cells
  • Examples: humans, animals, plants
  • Cells need to communicate and coordinate to function properly

Tissues and Organs

• Tissue:
  • A collection of cells that perform the same function
  • Examples: muscle, nerve, connective, epithelial tissue
• Organ:
  • A structure that contains more than one type of tissue working together
  • Examples: heart, stomach, brain
• Organ system:
  • A group of functionally related organs
  • Examples: digestive system, circulatory system

Hierarchical Structure of Organisms

• Cells:
  • The basic unit of structure and function in living organisms
  • Perform various functions, such as growth, metabolism, and reproduction
• Organelles:
  • Specialized structures within cells
  • Examples: chloroplasts, mitochondria, ribosomes
• Tissues:
  • A collection of cells that perform the same function
  • Examples: muscle, nerve, connective, epithelial tissue
• Organs:
  • A structure that contains more than one type of tissue working together
  • Examples: heart, stomach, brain
• Organ systems:
  • A group of functionally related organs
  • Examples: digestive system, circulatory system

Stem Cells and Differentiation

• Stem cells:
  • Cells that have the potential to form many other cells
  • Can be totipotent, pluripotent, or multipotent
• Differentiation:
  • The process by which cells become specialized for a specific function
  • Involves the expression of specific genes and the formation of specialized structures and organelles

Gas Exchange in Plants

• Stomata:
  • Tiny pores on the underside of leaves that allow for gas exchange
  • Regulated by guard cells
• Photosynthesis:
  • The process by which plants convert sunlight into chemical energy
  • Occurs in chloroplasts and requires carbon dioxide and water

Leaf Structure and Photosynthesis

• Leaf structure:
  • Includes the cuticle, upper epidermis, palisade mesophyll, spongy mesophyll, and lower epidermis
  • Each layer has a specific function, such as reducing water loss or capturing light for photosynthesis
• Photosynthesis:
  • Occurs in chloroplasts and requires light energy
  • Produces glucose and oxygen as byproducts### Plant Structure and Function
• A leaf's structure is adapted to increase light absorption and carbon dioxide diffusion:
  • Large surface area to increase light absorption
  • Thin to minimize distance for carbon dioxide diffusion
  • Chlorophyll absorbs sunlight and transfers energy into chemicals
  • A network of veins supports the plant and carries water and carbohydrates
  • Stomata (pores mainly located on the underside of the leaf) allow carbon dioxide to diffuse into the leaf
• Leaf adaptations:
  • Thin, transparent epidermis to allow more light to reach photosynthetic cells
  • Thin, waxy cuticle to protect the leaf, reduce water loss, and not block out light
  • Palisade cell layer near the top of the leaf to increase light absorption
  • Spongy mesophyll layer with spaces to allow carbon dioxide to diffuse into the leaf easily
  • Palisade cells contain many chloroplasts to absorb all available light

Photosynthesis and Starch

• The presence of starch in a leaf indicates that photosynthesis has occurred
• A leaf makes and stores starch, which can be tested for using iodine

Plant Systems

• The shoot system includes the leaves, stems, flowers, buds, and (potentially) fruit
• The root system includes the roots, which anchor the plant, absorb minerals and water, and increase surface area for absorption
• Root hair cells increase surface area for absorption
• Xylem vessels transport water and dissolved minerals throughout the plant
• Xylem is made up of dead cells that form long, hollow tubes
• Phloem vessels transport glucose and nutrients throughout the plant
• Phloem is made up of living cells that form a two-way transport system

Xylem and Phloem

• Xylem vessels:
  • Transport water and dissolved minerals
  • Unidirectional movement (up the plant)
  • Made up of dead cells
• Phloem vessels:
  • Transport glucose and nutrients
  • Bidirectional movement (up and down the plant)
  • Made up of living cells

Water Uptake and Transpiration

• Water uptake occurs through root hair cells, which have a large surface area and take in water and mineral ions by osmosis and active transport
• Water moves up the plant through the xylem vessels, driven by transpiration pull and cohesion-tension theory
• Transpiration is the process of water vapour loss from the leaves, regulated by stomata and influenced by temperature, humidity, wind, and light intensity
• Wilting occurs when the rate of water loss through transpiration exceeds the rate of water uptake from the roots

Investigating Transpiration

• Potometers can be used to measure transpiration rate and investigate factors affecting it
• Stomata regulate the opening and closing of the stomatal opening, controlling transpiration
• Environmental factors such as temperature, humidity, wind, and light intensity affect transpiration rate

Translocation of Materials

• Phloem vessels transport sucrose and amino acids, the products of photosynthesis, from the leaves to the rest of the plant

• Sucrose and amino acids are transported in the phloem tubes dissolved in water

• Phloem cells are connected end to end and contain sieve plates, facilitating the movement of substances

• Transport in the phloem is always from source to sink, depending on the needs of the plant### Vascular Tissue

• Vascular tissue consists of xylem and phloem, which transport carbohydrates, nutrients, and water in vascular plants.

Xylem

• Function: Transports water and minerals from roots to leaves and provides structural support.
• Structure:
• Tracheids: Long, thin cells for water movement.
• Vessel Elements: Short, wide cells forming tubes for efficient transport.
• Fibers: Add strength.
• Parenchyma: Involved in storage and lateral transport.
• Types:
• Primary Xylem: Formed during initial growth.
• Secondary Xylem: Formed during secondary growth in woody plants.
• Mechanism: Water is pulled up through cohesion-tension, driven by transpiration.

Plant Respiration

• Definition: Converts sugars into energy (ATP).
• Process:
• Glycolysis: Breaks down glucose in the cytoplasm.
• Citric Acid Cycle: Processes pyruvate in the mitochondria, generating electron carriers.
• Electron Transport Chain: Uses electron carriers to produce ATP.
• Importance: Provides energy for growth, maintenance, and metabolic activities.
• Influencing Factors:
• Temperature
• Oxygen availability
• Substrate availability
• Water status

Phloem and Translocation

• Function: Transports sugars, amino acids, and other organic nutrients from sources (typically leaves) to sinks (areas of growth, storage, or metabolic activity).
• Structure:
• Sieve Tube Elements: Main conducting cells, lack nuclei, connected end-to-end forming sieve tubes.
• Companion Cells: Support sieve tube elements, aid in loading and unloading of nutrients.
• Phloem Fibers: Provide structural support.
• Phloem Parenchyma: Involved in storage and lateral transport of nutrients.
• Translocation:
• Definition: The process of transporting nutrients through the phloem from sources to sinks.
• Mechanism (Pressure-Flow Hypothesis):
  • Source Loading: Sugars are actively transported into sieve tube elements at the source, reducing water potential and causing water to enter by osmosis.
  • Pressure Build-Up: The influx of water increases pressure within the sieve tubes, driving the flow of the sap.
  • Transport: The pressure difference drives the flow of the nutrient-rich sap through the phloem.
  • Sink Unloading: Sugars are actively or passively transported out of the phloem at the sink, increasing water potential and causing water to exit the sieve tubes, relieving pressure.

Importance of Vascular Plants

• Ecological Functions:
• Primary Producers: The foundation of food webs on land.
• Establish structure and habitat when creating a habitat.
• Impact biogeochemical cycles (carbon, water, and nutrient cycles).
• Economic Importance:
• Agriculture: Principal crops (corn, rice, wheat).
• Forestry: Paper and wood for building.
• Medicine: Source of therapeutic substances.
• Preservation:
• Biodiversity is vital to the health of an ecosystem.
• Endangered Species: Many are at risk due to habitat loss and climate change.