Bio unit 2

Cards (116)

  • The intestine has increased surface area in the form of folds, ridges, and a large intestine that allows for absorption of nutrients.
  • Amphibians:
    • Inactive amphibians use moist skin for gas exchange
    • Active amphibians use lungs
    • Surface is highly folded to increase surface area
  • Reptiles:
    • Reptilian skin impermeable to gases and can't be used as a respiratory surface
    • More efficient lungs than amphibians
    • Gas exchange exclusively in the lungs
    • Reptiles have ribs but no diaphragm
    • Ventilation aided by movement of the ribs by the intercostal muscles
  • Birds:
    • Warm-blooded
    • High respiratory rate for efficient gas exchange
    • Lungs small and compact made of numerous branching air tubes (bronchi)
    • Gas exchange occurs in the smallest air tubes (parabronchi) with extensive blood capillary network
    • Ventilation of lung brought about by movement of the ribs
    • Flight - action of wing muscles ventilates the lungs
  • Insects:
    • Terrestrial, live on land
    • Water evaporates from the body surface causing dehydration
    • Gas exchange occurs through spiracles running along the side of the body
    • Spiracles lead into a system of branched, chitin-lined air tubes (tracheae)
    • Ventilation of tracheal system through compression and expansion of the abdomen
    • Gas exchange takes place at the end of tracheoles
    • Muscle fibres connected to tracheoles never exceed 20 micrometres in diameter for rapid diffusion
    • Fluid levels in tracheoles decrease during flight for more surface area for gas exchange
  • Human respiratory system:
    • Lungs enclosed in the thorax
    • Trachea transports air to bronchi, then bronchioles, and finally alveoli for gas exchange
    • Lungs not muscular, need ventilation mechanism
    • Ventilation by negative pressure breathing
    • Gas exchange occurs in alveoli with extensive capillary network
    • Surfactant prevents alveoli collapse
  • Plants:
    • Main gas exchange surface is the leaf
    • Leaf blade thin and flat with large surface area
    • Waxy cuticle reduces water loss
    • Stomata allow gas exchange
    • Adaptations for photosynthesis include large surface area, orientation towards the sun, and transparent cuticle and epidermis
  • Roots:
    • Water and ions absorbed mainly through root hair cells
    • Functions of main root tissues: epidermis, cortex parenchyma, endodermis, pericycle, xylem, phloem, cambium
    • Mycorrhizae association increases surface area for absorption
  • Stem:
    • Functions of stem tissues: cuticle, epidermis, collenchyma, cortex parenchyma, pith parenchyma, sclerenchyma, xylem, phloem, cambium
    • Xylem transports water and ions, phloem transports products of photosynthesis
  • Xylem:
    • Transports water and ions from roots to the rest of the plant
    • Contains xylem vessels, tracheids, and xylem parenchyma
    • Water enters and leaves xylem vessels through pits
  • Phloem:
    • Transports organic molecules in plants
    • Contains sieve tubes and companion cells
    • Sieve tubes have little cytoplasm and few organelles
    • Companion cells support sieve tubes and aid in transport
  • Phloem sieve tube cells contain numerous mitochondria, rough ER, and a large dense nucleus
  • Companion cells and sieve tube elements are connected via plasmodesmata
  • End walls of phloem sieve tube cells are perforated by small pores called sieve plates
  • Strands of cytoplasm pass through these pores from one phloem sieve tube element to the next
  • Vascular bundles contain xylem, phloem, cambium, and other cells
  • Cambium is a meristematic tissue that can keep dividing by mitosis
  • Xylem cells include vessels and tracheids, while phloem cells include sieve tube elements and companion cells
  • Xylem cells are dead, while phloem cells are alive
  • Xylem cell walls are thick and contain lignin, while phloem cell walls are thin and contain cellulose
  • Xylem cell walls are impermeable, while phloem cell walls are permeable
  • Xylem cells have no cytoplasm, while phloem cells have cytoplasmic strands
  • Xylem transports water and mineral ions, while phloem transports products of photosynthesis like sucrose and amino acids
  • Direction of transport in xylem is from roots upwards, while in phloem it is to and from sites of photosynthesis/storage to growing regions and sites of storage
  • Water uptake by roots can occur through apoplast, symplast, and vacuolar routes
  • Ions are absorbed by plant cells through active transport and co-transport mechanisms
  • Root pressure can push water up the xylem against gravity
  • Cohesion-tension theory explains water movement in xylem
  • Transpiration is the main force that pulls water into roots and up stems
  • Factors affecting rate of water uptake in plants include temperature, humidity, wind speed, and light intensity
  • Hydrophytic adaptations include floating leaves and stems for plants living in water
  • Adaptations of hydrophytes include:
    • Floating leaves and stems
    • Large air-filled cavities in leaves and/or stems enable plants to float and act as reservoirs of oxygen/carbon dioxide
    • Increased leaf surface area for gas exchange and photosynthesis
    • Lack of protective tissues like waxy cuticles to reduce water loss
    • Roots are usually reduced in size and act mainly to anchor the plant
  • Translocation is the process of moving the products of photosynthesis from where they are made or stored to other parts of the plant
    • Carried out by the phloem
    • Mechanism of phloem transport is not well understood
    • Mass flow hypothesis (pressure flow hypothesis) proposed by Ernst Munch in 1930
  • Details of how scientists believe the mass flow hypothesis works in plants:
    • Glucose produced during photosynthesis is converted into sucrose
    • Sucrose is passed into phloem sieve tubes through various routes
    • Increased sucrose concentration in sieve tubes reduces Ψ of sieve tube contents
    • Water moves into sieve tubes from xylem through osmosis
    • Roots and growth points act as sinks where sucrose is unloaded and converted into glucose/starch/other carbohydrate
  • Alternative theories to explain translocation:
    • Electro-osmosis: sieve plates become charged due to movement of water and ions, attracting/repelling substances
    • Cytoplasmic streaming: strands of cytoplasm move within cells and in different directions
    • Protein contraction/peristalsis: protein microtubules in sieve tubes contract and push cytoplasm along in different directions
  • The lifecycle of a potato plant:
    • Leaves act as source in summer
    • Potato tubers act as sink
    • Buds grow in autumn/winter and become sink
    • Shoots grow in spring, tubers are source of energy/nutrients until leaves develop for photosynthesis
    • All parts of plant are sink during summer growth
    • Tubers act as source at night
  • Investigating translocation:
    • Ringing experiment: removing bark and phloem from stem affects transport
    • Use of radio-isotopes: exposing leaves to radioactive CO2 to track transport
    • Use of aphids: feeding on phloem contents to analyze composition
  • Circulatory system in animals:
    • Closed circulation system: blood travels through vessels with heart as pump
    • Open circulation system: blood bathes all cells and organs, no red blood cells to transport oxygen
    • Single circulation: blood passes through heart once in each circulation, found in fish
    • Double circulation: blood passes through heart twice in one circulation, found in humans and mammals
  • Blood vessels and heart structure:
    • Arteries take blood away from the heart
    • Veins take blood into the heart
    • Capillaries are site of gas exchange and tissue fluid formation
    • Arteries have thick tunica externa, muscle, and elastic tissue to carry blood at high pressure
    • Arterioles constrict and dilate to control blood flow to capillaries
    • Capillaries consist of a single layer of endothelial cells
  • Capillaries:
    • Consist of a single layer of endothelial cells and are a tissue rather than an organ
    • Site of gas exchange with a short diffusion path
    • Capillary beds have a massive surface area for diffusion
    • Pressure is lowered as blood passes through capillaries due to greater cross-sectional area compared to arterioles
    • Capillaries are narrow, leading to greater resistance and slower blood flow, allowing more time for gas exchange
    • Red blood cells have to bend to squeeze through capillaries