biology plant respiration

explain how the structure of the leaf is adapted for gas exchange

• Large surface area for diffusion provided by the internal surfaces of the spongy mesophyll cells

• Short distance that the gases have to diffuse across from the photosynthesising cells to the air spaces in the leaf

• Presence of stomata in the leaf surface (mostly the lower surface, to protect from rain, sun and wind)

Inhalation

• The diaphragm contracts and flattens in shape

• The external intercostal muscles contract making the ribs move upwards and outwards

• The volume of the thorax increases therefore the air pressure decreases

• The pressure of the air outside the body is now greater than the pressure of the air in the lungs

• Gas flows from higher pressure to lower pressure (outside into lungs)

• As a result air flows into the lungs

• It is an active process (energy is required) because muscles are contracting

The air passes into the mouth, down the trachea, bronchi, bronchioles and then into the alveoli by diffusion.

Exhalation

• The diaphragm relaxes and becomes dome shaped

• The external intercostal muscles relax making the ribs move downwards and inwards

• The volume of the thorax decreases therefore the air pressure increases

• The pressure of air outside the body is now less than the pressure of air in the lungs

• Gas flows from higher pressure to lower pressure

• As a result, air flows out fo the lungs

• It is a passive process because muscles are relaxing

how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries

• Alveoli where oxygen and carbon dioxide diffuse in and out of the blood.

• Alveoli adapted for efficiency at exchanging gases by diffusion by having:

• Thin permeable walls so diffusion distance between air and blood is short (wall of alveolus is one cell thick)

• A moist surface in which gases dissolve

• Large surface area, hundreds of millions of alveoli giving a surface area of around 70m2 for diffusion (350 million alveoli per lung)

• High concentration gradients for gases because blood is continually flowing past delivering excess CO2 and taking on additional O2 and because of ventilation of the lungs which refreshes the air in the air sacs

• Each root hair is a single specialised cell of the root epidermis. The long thin outer projection of the root hair cell penetrates between the soil particles reaching the soil water  

• The soil water contains mineral ions but the concentration is lower than the concentration of solutes inside the root hair cell.   

• Soil water has a higher water potential so water moves into the root hair cell by osmosis 

• This water dilutes the contents of the root hair cell and increases its water potential so water moves from root hair cell into root cortex by osmosis.  

• In this way a water potential gradient is set up across the root cortex allowing water to be taken up by the xylem in the centre of the root