Overview For Biology

• Gas exchange


  The diffusion of gases (oxygen and carbon dioxide)
• Sites of gas exchange in humans


  • Lungs (alveoli)
  • Capillary beds in the body tissues
• Alveoli


  • Very large surface area
  • Good blood supply
  • Very thin walls
  • Position deep in lungs
• Alveoli have moist walls and are one cell thick
• Ventilation (breathing) system


  Maintains a large concentration gradient between the alveoli and the blood
• Gases move across the gradient

  From high to low concentration (low in the alveoli)
• As blood moves past the alveoli


  There is a constant change in O2 and CO2 concentration
• Breathing in


  1. CO2 concentration in alveoli LOW

  2. O2 concentration in the alveoli HIGH

  3. Diffuses into the blood
• Breathing out


  1. CO2 concentration in alveoli LOW

  2. Diffuses out to the blood
• Air moves in and out of the lungs


  Due to changes in air pressure
• Inspiration


  Movement of air into the lungs
• Expiration


  Movement of air out of the lungs
• Diaphragm


  A dome shaped muscle that separates the thoracic and abdominal cavities
• When diaphragm contracts


  The dome flattens and the volume of the thoracic cavity increases
• Organs involved in ventilation(process by which air moves)

  • Mouth/nose
  • Pharynx (throat)
  • Larynx (voice box)
  • Trachea (windpipe)
  • Two bronchi
  • Bronchioles
  • Alveoli
• Alveoli walls


  • Very thin (one layer of cells)
  • Surrounded by a dense network of capillaries
• Haemoglobin + O2


  Oxyhaemoglobin
• Gas exchange:  The macroscopic structure that facilitates gas exchange is the lungs, the microscopic structure is alveoli.
•  The dissolved gases of oxygen and carbon dioxide move by diffusion:
• ventilation: movement of air into and out of the lungs in two stages inspiration and expiration, controlled by the diaphragm and ribcage.
• gas exchange; The exchange (diffusion) of oxygen and carbon dioxide to and from the blood at the alveoli and the respiring tissues.
• One is where your heart and lungs live (this is called the thoracic cavity), and the other is where your stomach, liver, and other organs live (this is called the abdominal cavity).
• The alveoli are like millions of tiny bubbles inside your lungs. Even though each alveolus is really small, having so many of them means they cover a huge area altogether. This big surface area is super important because it gives your lungs lots of places where oxygen can get into your blood and carbon dioxide can get out of your blood.
• Cystic Fibrosis


  A genetic disorder affecting the respiratory, digestive, and reproductive systems, caused by a mutation in the CFTR gene and characterized by thick mucus production, respiratory infections, and malabsorption of nutrients.
• Trachea structure


  The windpipe is made up of C-shaped rings of cartilage that keep it open and allow it to bend
• Lung tissue in water

  It floats because it contains alveoli, which make it less dense than water
• Autotrophs


  Organisms that produce their own energy by converting solar energy (from the sun) into glucose in a process called photosynthesis. This glucose is then converted to energy in the form of ATP in a process called respiration.
• Main systems in plants

  • Root system
  • Shoot system
  • Reproductive system
• Root hair cells


  • Contain hair-like extensions to the membrane surrounding the root cells
  • Projection increases the surface-area-to-volume-ratio (SA:V) maximising the rate at which water diffuses from the soil into the plant by osmosis
  • This water is then transported to the leaves where it is used for photosynthesis. Root cells must also undergo cellular respiration to create the energy they need to grow and repair.
  • Long thin shape maximises the rate at which oxygen moves into the cell and carbon dioxide is removed
• Root hair cell function

  1. Absorb water by osmosis

  2. Undergo cellular respiration to create the energy they need to grow and repair
• Palisade mesophyll cells


  • Located on the upper side of the leaf just below the almost transparent cells of the upper epidermis
  • Coated in a waxy layer that prevents water loss
  • Where most of the photosynthesis within the leaf occurs
  • Tightly packed together and close to the surface of the leaf to maximise light absorption
  • Contain a lot of chloroplast which allow them to perform photosynthesis
• The waxy cuticle layer prevents gas or water from entering or leaving the leaf.
• Guard cells (stomata)


  • The only way gases and water vapour is able to be transported into/out of the cell is through pores in the epidermis called stomata.
  • Contain chloroplasts
  • Open and close to allow gases and oxygen to leave and enter the leaf
  • Respond to light, opening at day break and closing at night, and hydration levels
  • If the leaf is losing too much water the stomata will close, if it is humid and they are well hydrated the stomata remain opened
• Explain how guard cells can maintain balance within a leaf

  1. Observation: Guard cells are found on the surface of leaves in plants and are responsible for regulating the plant's water loss by closing and opening tiny pores called stomata.

  2. Linking statement: When the guard cells need to allow gas exchange for photosynthesis to occur they take up water, swell and become turgid opening the stomata, but when plants need to reduce water loss, the guard cells release water and become flaccid causing the stomata to close.

  3. Inference: This allows the plant to maintain the right balance of gas exchange and water loss.
• Plant adaptations


  • Waxy coating on epidermis - Prevents damage from UV radiation
  • Sunken guard cell - Regulation of water preventing loss preventing contact with air currents. Air gets trapped increasing humidity within the space and reducing the concentration gradient for osmosis to occur leading to lower transpiration rates
  • Allelopathic - Toxins are released into ground preventing growth of other plants surrounding it
• Explain how the structural features and location of sunken stomata in xerophytic plants contribute to reducing water loss

  1. Observation: In xerophytic plants, sunken stomata are a crucial adaptation for survival in arid environments.

  2. Linking statement: The structural features and location of sunken stomata function differently compared to typical stomata found in mesophytic plants.

  3. Inference: The sunken position of the stomata and the trapping of air around them reduces the concentration gradient for water loss, leading to lower transpiration rates and better water conservation in the xerophytic plant.
• Hair root cells absorb water effectively because of:


  - Many root hairs increasing surface area - Thin cell walls allowing easy water passage - Osmosis drawing water from soil into the plant
• Palisade Mesophyll Cells


  Found in the upper part of a leaf, long and tightly packed together, packed with chloroplasts that capture sunlight, help plant make food through photosynthesis using sunlight, water, and carbon dioxide.
• Carbon Dioxide Transport in Plants

  CO2 enters the plant through stomata, diffuses into cells by osmosis, fixed via Calvin Cycle, and transported through Phloem tissue
• The two main vascular tissues in plants are xylem and phloem.