2c. Structure & Function in Living Organisms: Respiration, Gas Exchange

what is ATP?

during the process of cellular respiration, glucose is broken down and several molecules of ATP are produced

ATP can be broken down to release energy for living processes

define aerobic respiration

the chemical reaction in cells that uses oxygen to break down nutrient molecules to release energy

it involves the complete breakdown of glucose to release a relatively large amount of energy

carbon dioxide and water are produced as waste products, as well as releasing useful cellular energy

define anaerobic respiration

the chemical reaction in cells that breaks down nutrient molecules to release energy without using oxygen

it involves the incomplete breakdown of glucose and so releases a relatively small amount of energy

different breakdown products are formed depending on the type of organism that the anaerobic respiration is taking place in

how/why does anaerobic respiration take place in animals?

• takes place in muscle cells during vigorous exercise

• when we exercise, muscles have a higher demand for energy

• our bodies can only deliver so much oxygen to our muscle cells for aerobic respiration

• when oxygen runs out, glucose is broken down without it, producing lactic acid instead

• glucose has not been fully broken down, meaning there is still energy stored within the bonds of lactic acid

  • lactic acid builds up in muscle cells and lowers the pH of tissues

    • acidic conditions can denature the enzymes in cells

  • it will eventually be broken down using oxygen to produce carbon dioxide and water as waste products

how does anaerobic respiration take palce in plants and fungi?

• plants and yeast break down glucose without oxygen to produce ethanol and carbon dioxide

• anaerobic respiration in yeast cells is called fermentation

  • fermentation is important in the manufacture of bread and brewing

how are aerobic and anaerobic respiration different?

in terms of oxygen, glucose breakdown, products, and energy released

PRACTICAL: Demonstrating the production of carbon dioxide

METHOD

• measure out 10cm³ of hydrogencarbonate indicator into 3 boiling tubes

• put in a layer of cotton wool

• place 10 germinating seeds in tube A

• place 10 boiled/dead seeds in tube B

• place 10 glass beads in tube C

• seal each gube with a rubber bung

• after 3 hours, observe the colour of the indicator

HYDROGENCARBONATE INDICATOR

• red in atmospheric CO₂ levels

• yellow in high CO₂ levels as it dissolves in water and forms carbonic acid

• purple in low CO₂ levels as the solution turns more alkaline

RESULTS

• Tube A should turn yellow as the seeds are respiring and producing CO₂

• Tube B should remain red as the dead seeds produce no CO₂

• Tube C should remain red as there is no living material in them

PRACTICAL: Demonstrating the production of heat

METHOD

• set up the flasks as shown in the diagram

  • Flask A with dead seeds

  • Flask B with germinating seeds

• make sure the cotton wool is plugging the top of each flask

• hold the thermometer in place with the cotton wool

• invert the flask

• record the initial temperature

• after 4 days, record the final temperature

RESULTS

• the thermometer in Flask B should show an increase in temperature

• Flask A should remain at room temperature

• this is because the seeds in Flask B are respiring and producing thermal energy in the process

• this shows that respiration is an exothermic reaction

• the seeds in Flask A are not respiring because they are dead, so the temperature remains the same

how does diffusion occur in single-celled vs multicelled organisms?

single-celled: through the cell membrane, as there is a very short diffusion distance

multicellular: through exchange surfaces and organ systems

how does gas exchange occur in respiration?

• oxygen diffuses down the concentration gradient from outside the leaf to inside the leaf

  • cells use oxygen in respiration, so the O2 concentration inside leaves is always low

• carbon dioxide diffuses down the concentration gradient from inside the leaf to outside the leaf

what adaptations do leaves have to maximise gas exchange?

externally + internally

• thin: gives a short diffusion distance

• flat: provides a large surface area to volume ratio

• have many stomata: allow movement of gases in and out of the air spaces by diffusion

• adaptations of the internal leaf structure/tissues include:

  • Air spaces to allow gas movement around the loosely packed spongy mesophyll cells

  • Many stomata in the lower epidermis open in sunlight to allow gas movement in and out of the leaf

  • Thin cell walls allow gases to move into the cells easily

  • Moist air which gases can dissolve into for easier movement into and out of cells

  • The close contact between the cells and the air spaces allows efficient gas exchange for photosynthesis and respiration

what are stomata and guard cells and how do they work?

• stomata are spaces found between two guard cells predominantly on the lower epidermis of the leaf

• guard cells are responsible for the opening and closing of the stomatal pore which controls gas exchange and water loss

• Stomata open when water moves (by osmosis) into the guard cells causing them to become turgid

  • This allows gases to diffuse in and out of the leaf through the stomatal pore

  • Stomata tend to open when there is plenty of water and sunlight

• Stomata close when the guard cells lose water (by osmosis) to the neighbouring epidermal cells and they become flaccid

  • This prevents any diffusion into or out of the leaf

  • Stomata tend to close due to low water availability or low sunlight

how does gas exchange in plants differ at night and day?

• in the daytime, plants both respire and photosynthesise

  • the rate of photosynthesis tends to be higher than the rate of respiration

  • therefore there is a net diffusion of co2 into the plant and a net diffusion of oxygen out of the plant

• during the nighttime, plants only respire

  • there is a net movement of oxygen into the plant and a net diffusion of carbon dioxide out of the plant during the nighttime

why does gas exchange in plants differ at night and day?

• plants can only photosynthesise when they have access to light, but cells respire all the time

how does gas exchange occur in plants at low light intensitites?

• the rate of photosynthesis is equal to the rate of respiration

• this means that there is no net movement of oxygen or carbon dioxide in either direction

what are the structures of the respiratory system?

the thorax is the human chest cavity, and it consists of:

• the lungs

• the ribs

• intercostal muscles

• diaphragm

• trachea

• bronchi

• bronchioles

• alveoli

• pleural membranes

what adaptations do the lungs have to maximise gas exchange?

• large surface area to allow for faster diffusion of gases

• thin walls to ensure short diffusion distances

• good ventilation with air to maintain a steep concentration gradient

• good blood supply to maintain a steep concentration gradient

what is the function of the ribs?

bone structure that protects internal organs such as the lungs

what is the function of the intercostal muscles?

muscles between the ribs which control their movement, causing inhalation and exhalation

what is the function of the diaphragm?

sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inahlation and exhalation

separates the chest cavity from the abdomen

what is the function of the trachea?

windpipe that connects the mouth and nose to the lungs

what is the function of the larynx?

also known as the voice box, when air passes across here we are able to make sounds

what is the function of the bronchi?

large tubes branching off the trachea with one bronchus for each lung

what is the function of the bronchioles?

bronchi split to form smaller tubes called bronchioles in the lungs connected to alveoli

what is the function of the alveoli?

tiny air sacs where gas exchange takes place

what is the function of the pleural cavity?

the fluid filled space between the pleural membranes which reduces friction and allows the lungs to move freely

how do the intercostal muscles move?

• the two sets of intercostal muscles work antagonistically

  • external intercostal muscles contract to pull the rib cage up during inhalation

  • internal intercostal muscles contract to pull the ribcage down during forced exhalation

what happens during inhalation?

what happens during normal exhalation?

• external intercostal muscles relax

• ribcae moves down and in

• diaphragm relaxe

what happens during forced exhalation?

how are the alveoli adapted and specialised for gas exchange?

• there are many rounded alveolar sacs which give a large SA:V ratio

• alveoli (and the capillaries around them) have thin, single layers of cells to minimise diffusion distance

• ventilation maintains high levels of oxygen and low levels of carbon dioxide in the alveolar air space, leading to a steep concentration gradient

• good blood supply ensures a constant supply of blood high in carbon dioxide and low in oxygen to maintain concentration gradients

• a layer of moisture on the surface of the alveoli helps diffusion as gases dissolve

what harmful chemicals are in cigarettes and what do they do?

• nicotine

  • narrows blood vessels and increases heart rate, leading to increased blood pressure

  • leads to blood clots forming in arteries, resulting in heart attacks or strokes

• carbon monoxide

  • binds irreversibly to haemoglobin, reducing the capacity of blood to carry oxygen

  • puts strain on the breathing system, as breathing freqency and depth need to increase to supply the same amount of oxygen

  • the circulatory system needs to pump blood faster, raising blood pressure and increasing the risk of coronary heart disease or stroke

• tar

  • is a carcinogen linked to increased chances of cancerous cells developing in the lungs

  • contributes to COPD, which occurs when chronic bronchitis and emphysema occur together

what is chronic bronchitis?

• tar stimulates goblet cells and mucus glands to enlarge and produce more mucus

• mucus builds up, blocking the smallest bronchioles and leading to infections

  • the build-up of mucus can result in damage to the cilia, preventing them from beating and removing the mucus

• a smoker’s cough is the attempt to move the mucus

what is emphysema?

• emphysema is a result of frequent infection

  • infections occur more frequently in smokers due to the build-up of mucus that occurs in the lungs

• phagocytes that enter the lungs release elastase, an enzyme that breaks down the elastic fibres in the alveoli

• the alveoli become less elastic and cannot stretch, so many burst

• the breakdown of alveoli reduces the surface area for gas exchange

• emphysema patients become breathless and wheezy, and may need a constant supply of oxygen to stay alive