Download Gas exchange in insects: trachea

Gas exchange in insects: trachea
• Insects have a series of air-filled tubes, trachea, that
provide oxygen to living cells. These trachea make up the
respiratory system of insects.
• Air enters the system via various inlets called spiracles and
move into the main trachea that continue to branch,
getting smaller each time, with tracheoles being the
smallest into the insect cells.
• Tracheole ends make direct contact with the body cell, and
oxygen diffuses from tracheoles across the membrane
• Gas exchange occurs similarly to vertebrates and fish,
whereby CO2 is exchanged for O2 via the process of
diffusion.
Comparing positioning of respiratory systems
• Complete Quick-check questions 11-16 on page 150.
Transport of wastes
• Metabolic activities produce wastes that
cannot be utilised by the body – in fact, they
have to be eliminated. This process is known
as excretion.
• The main wastes that are generated by
metabolic activities and need to be excreted
are:
» Carbon dioxide – excreted via the lungs as a waste
product of cellular respiration
» Nitrogenous wastes such as urea – excreted via the
kidneys in the urinary system
Nitrogenous wastes in animals
• When animals metabolise protein, nitrogen-containing compounds
are produced as wastes – called nitrogenous wastes. These need to
e excreted as they can cause damage to tissues if they are left to
accumulate.
• Different animals excrete different forms of nitrogenous waste,
depending on the environment they live in.
• When protein is metabolised, it initially produces ammonia, a very
toxic form, which must be excreted immediately and can only be
excreted in this form if the animal lives in water – fish excrete
ammonia.
• In organisms without a ready supply of water, the ammonia must
be converted to a less toxic form of nitrogenous waste – called
urea. Mammals excrete urea. This conversion requires energy.
• Another form, uric acid, is excreted by birds and reptiles. It requires
lots of energy but very little water to excrete this form.
The urinary system
• Most nitrogenous wastes are removed from the mammalian body
by the urinary system.
• Water is the most common compound in the body, and the urinary
system plays a significant role in maintaining water balance in
mammals.
• The urinary system is comprised of two kidneys, two ureters, a
bladder and a urethra.
• Figure 6.38 – Components of
the human urinary system.
Kidneys - function
• Humans have two kidneys, flattened, bean-shaped organs
located on each side of the spine, partially protected by the
rib cage and embedded in a mass of fat for protection.
• Kidneys play a major role in the the balance of water in
mammals.
• Kidneys are adapted for filtering wastes (including
nitrogenous wastes) from the blood. They also excrete
hormones and other substances such as vitamins that
would otherwise build up in the body.
• Kidneys also maintain a correct balance of ions in the blood
by excreting those that are in excess, which helps maintain
the pH of the blood.
Kidneys - structure
• The outer-most layer of kidney tissue is called the cortex, a
granular-looking layer that extends into the second, striated layer,
the medulla. The functional units of the kidney, nephrons, are
found in these regions.
• Each kidney contains about one million nephrons. It is the process
of filtration and reabsorption that regulates the body fluid
composition.
• The artery that enters the kidney, the renal artery, branch into
smaller and smaller arteries and then eventually into capillaries.
These capillaries form small clusters, called glomerulus.
• Each glomerulus is surrounded by a double walled cup, known as a
Bowman’s capsule, which forms part of the tubule. The remainder
of the tubule coils away from the glomerulus and eventually forms
a collecting tubule, part of which is the Loop od Henle.
• The arteriole that leaves the capillary network in
the glomerulus winds around the tubule before it
joins with the other vessels to form a vein that
leaves the kidneys.
Formation of urine
Formation of urine - task
• Read through the information under the sub heading
‘Formation of urine’ on pages 153 -154 as well as the
information in Figure 6.41 on page 154.
• Construct a table which summarises the three main
stages of the formation of urine:
– Filtration
– Reabsorption
– Excretion
• Pay particular attention to explaining the parts of the
nephron, the movement of molecules and the way
molecules are moving.
Hypertonic vs Hypotonic
• Mammals produce hypertonic urine – urine that contains a higher
concentration of solutes than do the body fluids of the same
animal.
• Other animals, for example freshwater bony fish and amphibians,
produce hypotonic urine – urine that contains a lower
concentration of salts than do the body fluids of that same animal.
• Hypertonic urine is said to be more concentrated, whereas
hypotonic urine is said to be more dilute.
• After it is formed, urine is carried away from the kidneys via the
ureters. Two ureters, one from each kidney, transport the urine to
the bladder, which stores the urine until it leaves the body. Urine is
transported from the bladder to outside the body by the urethra.
Excretion in fish
Summarise excretion in fish:
- compare saltwater fish to freshwater fish.
Excretion in insects (and spiders)
• Insects have specialised excretory organs called
Malpighian tubules. They extend into the body
cavity from the intestine and float freely in the
blood in the open circulatory system.
• Wastes and fluid pass from the blood into the
tubules where nitrogenous wastes are converted
into uric acid crystals.
• Material from the tubules is then emptied into
the intestine.
• Fluids are reabsorbed by the intestine and the
uric acid crystals are excreted through the anus.
Comparing systems in animals
Complete Quick-check questions 17-22 on page 157.
Transport in plants
• Plants transport materials in vascular tissue, which is
made of xylem and phloem.
• Xylem transports water and dissolved minerals. Some
minerals are found in relatively large amounts
(macronutrients) for normal growth. Other nutrients
are required in very small amounts, these are called
micronutrients or trace elements.
• Phloem transports sucrose, produced by
photosynthetic tissue, to other regions of the plant
that are non-photosynthetic. Hormones and any other
organic materials made by the plant also travel through
the phloem.
Xylem
• Water is absorbed by the root
hairs and moves up the xylem
vascular (called xylem
parenchyma cells) tissue via
the process of cohesion – the
water molecules tend to stick
together, being pulled up
through the hollow xylem cells
towards the leaves, where
they are required for
photosynthesis.
• Transpiration refers to the
movement of water
throughout the plant.
Phloem
• Soluble organic substances move through the phloem tissue, mainly
in the form of sucrose.
• These substances are moved from the leaves where they are
synthesised, to other parts of the plant where they are used or
stored.
• The transport of organic substances through the plant is called
translocation.
• Photosynthetic leaves produce sugars, so are the source of organic
matter for the rest of the plant.
• Sucrose is actively transported from phloem tissue into cells where
it is used in different ways. It can be:
– Stored as starch
– Stored as subunits for building structural components of cells
– Used as an energy source in cellular respiration (glucose)
Figure 6.48 – Summary of the processes of transpiration in
xylem tissue and translocation in phloem tissue.
• Complete Quick-check questions 23 and 26 on page 163.
Gaseous exchange in plants
• Many plants have specialised structures for gas exchange.
• Although some CO2 is produced by plant cells as they carry out
respiration, the amounts produced are far too insufficient for
adequate rates of photosynthesis – they require CO2 from the air.
• Stomata in the leaves are the main site for gas exchange in the
plant – comprised or a stoma and two guard cells.
• Each stoma (pore) is surrounded by two guard cells, that control
whether the stoma is open or closed.
• The shape of the guard cell is influenced by the amount of water
vapour in the leaves.
• When the guard cells have a high amount of water, they become
full or turgid, and the stoma opens.
• When the guard cells lose water, they become more flaccid and the
pore closes.
• Gases are not the only substance to move into and out of the
stomata – water vapour also leaves through the stoma. This
occurs at a greater rate on dry days where the humidity (water
vapour content of the air) is low.
• Some plants have specialised features to help reduce water
loss.
• Lenticels are specialised openings to allow gas exchange in
stems – to much less extent than stomata in leaves.
• Gaseous exchange also occurs in the roots, aided by the root
hairs – oxygen which is required for cellular respiration diffuses
in to the root hairs and carbon dioxide diffuses out.
Excretion in plants
• Unlike animals, plants have no specialised excretory
systems.
• They either use their waste or store the waste in a situation
that poses no problems or harm to the cells.
• In plants, the term ergastic substances is used instead of
excretory products. These substances include stored food
materials such as starch granules.
• Unwanted ions such as sodium and chloride remain in the
leaves that are shed by deciduous plants.
• Some plants have special features that enable them to
eliminate substances that have been absorbed from the soil
along with the water – demonstrating that plants can
remove unwanted substances.
Comparing plants with mammals
• The transport systems of plants and mammals have some
similarities – both are made up of a network of fine tubes
that penetrate tissues and come into close contact with
every cell and they each supply their tissues with nutrients,
but there are some important differences:
– Mammals require blood to carry and a heart to pump O2 to all
cells; plants lack an equivalent organ.
– Mammals have specialised pigmented cells, e.g. haemoglobin
to handle the increased O2 demands in animal cells; plants do
not have the same demands and therefore lack these. Most of
the O2 required by plants is obtained as a product of
photosynthesis.
– Bulk intake of food for energy in mammals produces large
amounts of toxic nitrogenous waste that must be eliminated
through a specialised excretory system; plants either use or
store any ergastic substance produced at no harm to cells.
Questions and revision
• Complete Quick-check questions 27-30 on page
167.
• Complete Quick-check questions 31-32 on page
169.
• Biochallenge question 1 on page 170.
• Complete the following Chapter Review questions
on pages 171-173.
– 3, 6, 7, 11, 13 and 14