gas exchange in leafs

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What is a stomata?

On the underside of the leaves are small holes or pores, called stomata. A single hole is a stoma.

each stomata is srounded by 2 guard cells these control the opening and closing of the stomata

when co2 levels drop inside the plant the guard cells gain water and become turgid. opening the stomata allowing gases in and out. water also avaporates through the stomata

high carbon dioxide levels cause the guard cells to lose water they become flaccid when closing the stoma. water moves in and out of the guard cells as potasium k+ ions move.

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cells differentiation

is the process by which cells become specialised for different functions. different genes are switched on and off in each of the specialised cells

how they differ?

  • In shape= a neurone is long and thin with an insulating sheath while RBC is a concave disc with no nucleus
  • In type and number of each of the organelles= muscles and sperm cells contain many mitrochondria while a bone cell have very few = a white blood cell have many lysosmes while a muscle cell has very few

this has occured through evolution but means that some cells functions have been lost as the cells becomes a specialised cell

it occurs durring the development of the embryo by the genes being repressed (switched off)

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human and plants tissus and organs

tissues = a collection of cells (not necessarily identical ones) that perform a specific function

examples: epithelial tissues in alveoli, trachea,small intestine; line the surface of organs and often have a protective or secretory function. xylem tissues made of a number of cell types used for transporting water and mineral ions ina plant

organs= a combination of tissues that are coordinated to perform a variety of functions


stomach is made of muscle tissue to churn and mix contents, epithelial tissue is to secrete digestive juices and HCL and the stomach wall, connective tissues hold together the selection of tissues

leaf is made of palisade mesophyll; to carry out photosynthesis, spongy mesophyll; to enable adequate gas diffusion, epidermis (upper and lower); to protect the leaf, phloem; to transport organic material away from the leaf (glucose), xylem; to transport water and ions into the leaf

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organ systems

They work together as a single unit


digestive system= salivary glands,oesophagus,stomach,duodenum, ileum, pancreas and liver

respiatory system= lungs, trachea and bronchi

circulatory system= heart, arteries and veins

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gaseous exchange in lungs

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breating (ventilation)

Air is to be constantly moved in and out of the lungs

if the air pressur outside is bigger than the air pressure inside the lungs air is forced INTO the lungs

if air pressure outside is smaller than the air pressure inside the lungs air is forced OUT of the lungs

these pressure changes are brought about by the movement of 2 sets of muscles

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an active process which requires energy

external intercostal muscles contract

internal intercostal muscles relax

the ribs are pulled up and out increasing the volume of the thorax

diaphram muscles contracts = flattens out and pulls down = increasing the volume of the thorax

air pressure inside the lungs decreases= air pressure outside is greater therefore air is forced into the lungs

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mostly passive - requires little energy

elastic lungs recoil = forces air out

internal intercostal muscles contract

external intercostal muscles relax

the ribs move down and in = decreasing volume of thorax diaphram muscles relaxes=moves up into dome position = decreasing volume. Air pressure in lungs increases Air pressure inside is now greater than the air pressure outside, therefore air is force out of the lungs.

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pulmonary ventilation

is the total volume of air that is moved into the lungs during 1 minute

tidal volume = volume air normally breathed in when at rest

ventilation rate = the number of breathes within 1minute

pulmoary ventilation= tidal volume  x ventilation rate

dm3 min-1                  dm3                    min-1

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