Multicellular Organisms Flashcards
1
Q
Unicellularity
A
- unicellular organisms such as protozoans are complete functioning organisms. The microscopic size of the cell allows three processes to occur efficiently
- a single cell has a high surface area to volume ratio. This means that the size of the plasma membrane (its surface area) is sufficient to service the total volume of the cytoplasm
2
Q
Multicellularity
A
- the evolution from unicellular organisms to multicellular organisms required three organising principles:
- cell division - so that many cells are created
- specialisation - (of function) of cells
- communication with other cells
3
Q
How do plant cells specialise?
A
- unlike animals, many plant cells retain the ability to differentiate and specialise throughout their life. These cells are formed in tissues called meristems
- meristematic cells undergo mitosis allowing the plant to grow and are the only places in plants where cells divide
- they are found at the tips of roots and shoots and in a ring around the inside of stems and branches
4
Q
Levels of organisation
A
- organisation is a defining feature of living things
- organisms are organised according to a hierarchy of structural levels
- the cells together form tissues and tissues together form organs, which make up all the different part of the multicelllular organism
- atom, molecule, cell, tissue, organ, organ system, organism
5
Q
Types of plant cells
A
- parenchyma cells - majority of plant cells. They carry out photosynthesis and cellular respiration, store starch and proteins and play a role in repair
- collenchyma cells - provide support and structure to growing plants
- scierenchyma cells - hard (dead) cells with thick secondary walls that support areas of the plants no longer growing
- xylem cells - transport water
- phloem cells - transport nutrients
6
Q
Plant tissues
A
Three main layers of tissue:
- Epidermis or dermal tissue - the “skin” of the plant. Thin layer of tightly packed cells that line and protect the plant
- ground tissue - the bulk of the plant tissue, contains the photosynthetic cells and storage
- vascular tissue - the transit system made up of the xylem and phloem cells
7
Q
Plant systems
A
- individual cells are organised into tissues (such as photosynthetic tissue), which form the organs (such as the leaf) of the plant body. Each of these tissues is specialised to perform important functions
- these include obtaining energy, producing organic compounds, distributing materials, removing wastes and exchanging gases
- the structure of a vascular plant ensures that each organ - the leaves, stem, roots, flowers and seeds - receives what it needs
- the shoot system is composed of all parts of the plant found above ground. It is responsible for the transportation of resources, the absorption of oxygen and carbon dioxide, reproduction and carrying out photosynthesis in leaves
- the root system is below ground and is responsible for absorbing water and nutrients from the soil
8
Q
Non-vascular plants
A
- non-vascular plants do not have vascular tissue, no xylem or phloem
- they do not have root-like, stem-like and leaf-like structures
- root-like structures called rhizoids are elongated cells that attach the plant to the soil
- they are normally found in moist environments, where they absorb water and nutrients from. They have a cuticle to prevent water loss.
- best example of non-vascular plants are mosses
9
Q
Vascular plants
A
- land-based plants had to evolve systems for transporting resources from one part of the plant to another
- all plants need to be able to get water to their leaves. Water is absorbed initially by the roots and moves against the pull of gravity through the stem to the leaves. When we look at how that occurs, we find the plant is best serviced by a one-way water movement system - the xylem
- xylem carries water and dissolved nutrients from the roots to the rest of the plant
- phloem transports sugars and other products from where they are produced, often in the leaves, to the rest of the plant
10
Q
Vascular vs non-vascular plants
A
Vascular plants
- has roots, stems and leaves
- has vascular bundles - can transport water
- larger in size
- is better able to store water in cells
Non-vascular plants
- doesn’t have root-like, stem-like and leaf-like structures
- non vascular bundles - are unable to transport water
- smaller in size
- must live in damp conditions
11
Q
Water movement : xylem
A
- water and mineral transport from roots to other parts of the plant
- unindirectional - moves up the plants stem
- found in the roots, stems and leaves and occupy the centre of the vascular bundle
- mature xylem are made up of dead cells
12
Q
Transporting water - the root system
A
- as well as anchoring the plant, the roots provide the surface through which water is taken up
- this surface area is greatly increased by the presence of thousands of root hairs projecting from the epidermis. A plant root hairs present an enormous surface area across which water is absorbed. This can be up to 130 times greater than the surface area of its shoot system
- water must reach the xylem by first passing through the epidermis and the ground tissue
- the main cells which make up the root are the cells of the ground tissue called parenchyma cells. At the centre of these cells is a xylem and phloem network of tubules
- water and dissolved minerals enter the root from the soil by the process of osmosis in the case of water molecules, and diffusion and active transport in the case of dissolved ions
13
Q
Functions of roots
A
- roots absorb water and minerals
- supports and anchors the plant
- storage tissue
- tap roots and fibrous roots
14
Q
Plants can have all different types of roots systems. There are two main types of roots:
A
- tap root system - large, tapering main root, with some short side branches. Tap roots push vertically down into the soil to reach the water. Found in eucalyptus and daises
- fibrous roots - small roots of equal size growing from the bottom of the plant. They do not grow deeply but do not help to hold the top layers of the soil together and prevent erosion. Found in coastal plain plants and grasses
15
Q
Transport water - the shoot system
A
- these tissues, along with phloem tissue, are grouped into a series of vascular bundles, each rather like an electric cable in the stem
- in the dicotyledon eucalyptus, for example, the vascular bundles are arranged in a ring towards the outside of the trunk. In monocotyledon plants such as lilies and grasses, they are scattered randomly throughout the stem
- the veins that are visible in a leaf are in fact vascular bundles
- root pressure forces water into the shoot system. From here other forces act to push water through to the whole plant
- water and minerals are moved through xylem due to a combination of root pressure and transpirational pull. Adhesion and cohesion assist with this journey
- the constant upwards movement is driven by the evaporation of water (transpiration) from the leaves
- the sun is also essential to this process as it creates the evaporation of water from the leaves to the atmosphere, and therefore promotes the forever that act on the water in the stem
16
Q
Structure of the xylem
A
- there are two types of transport tubes - vessels and tracheids
17
Q
Root pressure
A
- the forces of water entering the root and pushing its way into the cells creates pressure. This force is known as root pressure
- this pressure is what forces water up through the roots to the shoot system of the plant
18
Q
Adhesion force
A
- push water up the stem and into the leaves
- the force by adhesion is defined as the force of attraction between different substance, such as glass and water
- if you observe water in a glass cylinder the sides of the water push up against the side. The narrower the cylinder the higher water pushes up
- xylem tubes are extremely narrow so water can climb a considerable distance up the tubes
19
Q
Cohesion force
A
- The force of cohesion is defined as the force of attraction between molecules of the same substance
- this force pulls the water molecules together helping to maintain the column of water moving up the shoot system
- the force and pressure created by the two forces of adhesion and cohesion are very strong. The xylem is very tough and made of thick walls to help stand this force
20
Q
Transpiration
A
- the continuous column of water through the plant is known as the transpiration stream
- transpiration is the process by which moisture is carrier through plants from roots to small pores on the underside of leaves, where it changes to vapour and is released to the atmosphere
- essentially evaporation of water from the plant
- this constant loss of water from the leaves creates a transpirational pull of water from the root through to the leaves
21
Q
Factors that effect transpiration
A
High humidity - decrease
High temperature - increase
Large amount of light - increase
Strong winds - increase
22
Q
Transport of water - conserving water
A
- if the water loss via transpiration exceeds supply through the roots, the plant wilts
- the loss of water from the leaves causes the water column tension in xylem to rise and the water potential gradient between soil and xylem to increase, which allows roots to access more water
- when water flow to the roots slows, leaf stomata close rapidly to minimise water loss through transpiration
23
Q
Obtaining and transporting nutrients
A
- nutrients refer to substance such as minerals and vitamins. Plant nutrients are soluble minerals and salts such as sodium, potassium and phosphorus. These are required for the complex chemistry that runs every cell
- minerals are actively transported, or pumped, into the root hairs and other surface cells in the hound or growing parts of the root
- the nutrients then move between cells through the plasmodesmata (the microscopic channels which reverse the cell walls and connect the gaps between cells)
- once nutrients are inside the vessels and tracheids, they are carried up the stem along with the water in the transpiration stream. Once again the xylem is involved
- once the mineral ions reach the leaf they are used to produce more chlorophyll, proteins, carbohydrates and other minerals
- the transpiration stream does not use or require energy to operate
24
Q
Leaf structure and function
A
- thin and flat, present a large surface area to the light
- leaf shape is maintained by the turgor (rigidity) of the living cells inside them, the midrib and veins that are well supplied with stengthening tissues
- the midrib and veins consist of vascular tissue, the xylem and the phloem
- the large surface area of leaves, allows maximum photosynthesis, but increases evaporative water loss
- this is overcome by the presence of an impermeable waxy cuticle on the leaf surface
- stomata are minute aperture structures on plants found typically on the outer leaf skin layer (epidermis)
- stomata consists of two specialised cells, called guard cells that surround a tiny pore called stoma
- guard cells are cells surrounding each stoma. They help to regulate the rate of transpiration by opening and closing the stomata
- stomata allow diffusion of carbon dioxide and oxygen in and out of the plant cells
- the vascular tissues carry water, minerals and organic compounds throughout the plant
- every leaf cell is close enough to the vascular tissues to supply water via osmosis
25
Transporting from the leaves
- the xylem delivers the nutrients and water to all parts of the plant and especially to the leaves for photosynthesis
- photosynthesis only occurs in the leaves, so the sugars (sucrose) produced by photosynthesis must then be transported form the leaves to the rest of the plant, especially back to the roots
- the is the job of the second transport system in plants called the phloem
- this transport of sugar is called translocation
26
Phloem
- transportation of food and nutrients such as sugar and amino acid from leaves to storage organs and growing parts of the plant
- biodirectional - moves up and down the plant system
- roots, stems and leaves transport sucrose to growth (roots and shoots) and storage regions of the plant (seeds fruit and swollen roots)
- phloem occur on outer side of the vascular bundle
- made of living cells
27
Phloem structure
- the phloem consist of conducting cells (sieve cells), parenchyma cells and supportive cells
- sieve elements
- sieve plates
- companion cells
- the sieve tube and companion cells are connected via a plasmodesmata, a microscopic channel connecting the cytoplasm of the cells, which allows transfer of the sucrose, proteins and other molecules to the dive elements. The companion cells are thus responsible for fuelling the transport of materials around the plant
28
Sieve elements
- elongated, narrow cells, which are connected together to form the sieve tube structure of the phloem
- highly specialised
- unique in that they do not contain a nucleus at maturity and are also lacking in organelles = maximising available space for the translocation of materials
29
Sieve plates
at the connections between sieve member cells and sieve plates
- relatively large, thin areas of pores that facilitate the exchange of materials between the elements
- also act as a barrier to prevent the loss of sap when the phloem is cut or damaged
30
Companion cells
each sieve element cell is usually closely associated with a companion cell
- have a nucleus, are packed with dense cytoplasm contain ribosomes and many mitochondria
- companion cells are able to undertake the metabolic reactions and other cellular functions, which the sieve elements are therefore dependent upon the companion cells for their functioning and survival
31
Parenchyma
- is a collection of cells, which make up the ‘filler’ of plant tissues.they have flexible walls made up of cellulose. Within the phloem, the parenchyma main function is the storage of starch, fats and proteins
32
Waste removal in plants
- deciduous plants store wastes in leaves which drop off in autumn
- non-deciduous trees remove salt also be leaf fall
- plants with bark can transfer unwanted material via the phloem to the bark before shedding
- other waisted may be stored as insoluble crystals
- woody plants store watses in non-living tissue
- cell walls are used as a depository for toxins (lignin)
- waste removal act as resins, fats, waxes and complex organic chemicals, like latex from rubber trees
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Translocation
- is the net movement of sugars in solution through the plant
34
Plants need oxygen too
- plants obtain the gases they need through the surfaces, especially leaves
- they require oxygen for respiration and carbon dioxide for photosynthesis
Remember
- photosynthesis
- occurs in the cytoplasm
- energy produced (glucose)
- cellular respiration
- occurs in the cytoplasm and mitochondria
- energy produced (ATP)
35
Gas exchange in plants
- plants have specialised structures for gas exchange but not a specialised system solely devotes to it
- gas exchange is local and gases do not need to be transported through the plant
- in noon-vascular plants, gases move by simple diffusion in and out across the shot distance
- in vascular plants, oxygen and carbon dioxide are exchanged through the stomata or lenticels on leaves, stems and roots into and out of air spaced between cells
- remember plants need to get both oxygen and carbon dioxide in (unlike animals that only intake oxygen and expel carbon dioxide)
36
Gas exchange in vascular plants
- vascular plants absorb and release gases, including oxygen and carbon dioxide, via the stomata on the plant surface
- between the environment and the plant:
- gas exchange occurs through diffusion at the stomata
- within the plant:
- gas exchange involves the movement in and out of the intercellular spaces (spongy tissue)
- occurs via passive transport
37
Stomata
- are openings or “pores” in the leaf
- most abundant on the leaves, where they are usually found on the underside
- where diffusion of gases occurs
- O2 net movement out
- CO2 net movement in
- guard cells control whether they are open or not (to leave them open all the time would be inefficient)
38
Guard cells
- a pair of kidney-shaped cells
- guard cells are cells surrounding each stoma. They help to regulate the rate of transpiration by opening and closing the stoma
- the opening and closing of stoma is in response to water moving in and out of the guard cells
39
Regulating stomata
- when water moves in, the turgor (rigidity) of the guard cells increases causing them to swell and this opens the stomata
- the action that causes water to enter the guard cells is triggered by the uptake of potassium ions (K+) into the cells. This is stimulated by light hitting the leaves and potassium ions move into the guard cells by active transport
- this increases the concentration gradient so water enters by osmosis. The guard cells swell opening the stomata
- when K+ ions move out of the guard cells (in the dark), water leaves via osmosis, guard cells go limp and stomata close
- the opening and closing of the stomata can also be in response to carbon dioxide levels as the guard cells contain chloroplasts which produce glucose
- light plays an important role in regulation the opening and closing of the stomata. As such, stomata are generally open during the day and closed at night
- the movement of gases in leaves depends on simple diffusion and happens locally over short distances. No transport system is used
- plants need to balance their gaseous requirements with their ability to withstand water loss
- in drought - guard cells lose water and close stomata
- this reduces water loss but cuts CO2 supply
- this restricts photosynthesis
- and reduces overall plant growth
40
Why not leave the stomata open
- for gases to pass across the cell membrane they must be dissolved in water; thus a film of water must surround the guard cells. Therefore, plants are constantly losing water
- the loss of water is called transpiration
- without closing guard cells the plants would become very dehydrated
41
Sensitivity of stomata
- number and appearance of stomata depend on several environmental conditions
- moist (high humidity, high rainfall) = stomata open. Plants found in these climates also often have more stomata
- hot, dry weather with low humidity = more stomata closed. Plants found in these climates also often have fewer stomata. In some, the stomata are protected to reduce water loss
- low CO2 levels = stomata open
42
Gas movement through the plant
- once through the stomata simple diffusion spreads the gases to the other plant cells
- the cells of plants structures are loosely packed meaning that gas can diffuse through the spaces with no need for a transport system
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Beyond the leaf
- in the roots and stem gas exchange occurs in the outer layer of cells
- lenticels break through the bark and allow air to diffuse through
- lenticels are a porous tissue consisting of cells with large intercellular spaces. Found on the bar of woody stems and roots of flowering plants. It functions as a pore, providing a pathway for the direct exchange of gases between the internal tissues and atmosphere through the bark, which is otherwise impermeable to gases
- once inside the outer layers and within the plant, diffusion is used in the spongy tissue to spread the gases to all cells
44
Gas exchange in aquatic plants
- water plants have special adaptations to allow exchange of gases with their moist environment
- some plants (like water lilies) have their leaves floating in the water surface. They have their stomata in the stop surface of the leaf
- mangroves have aerial roots system above the water line
- submerged plants are able to exchange gases with the water across the epidermis
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Multicellular - cell specialisation
- all specialised cells originate from the stem cells
- stem cells differ from other cells in the body in three important ways:
- they are unspecialised (have not yet specialised into a particular type of cell)
- they have the potential to divide and replicate for long periods of time
- these relatively unspecialised cells can differentiate to from different specialised cells
- during early development of the embryo, cell layers migrate to different regions, genes are switched on or off in response to neighbouring cells and environmental cues
- cell appearance and function is determined by active genes (which are switched on)
- specialised cells are created
- in humans this results in 230 different types of cells
- the cells together form tissues and tissue together form organs, which make up all the different part of the multicellular organism
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Organelle level
- molecules associated with together to form complex, highly specialised structures and organelles within cells. e.g. Mitochondria, Golgi apparatus
47
Cellular level
- cells are the basic structural and functional units of organisms. Cells become specialised functions as a result of differentiation during development
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Tissue level
- tissues are composed of groups of cells of similar structure that perform particular related functions. Examples include: epithelial, liver tissue, bone, and kidney tissue
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Organ level
- organs are structures of definite form and structure, comprising two or more tissues. Examples include: kidneys, liver, heart, brain, lungs, stomach
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System level
- in humans and other animals, organs from parts of larger units known as organ systems. An organ system is an association of organs with a common function, e.g. digestion or excretion
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What do animals need to live
Make energy using:
- food
- oxygen
Animals build bodies using:
- food for raw materials (manufacturing amino acids, sugars, fats, nucleotides)
- ATP energy for synthesis
52
How do animals get their food
- filter feeding
- living inside their food
- fluid feeding
- bulk feeding
53
Different types of diets
All animals eat other organisms
- herbivores (e.g. gorillas, cows, rabbits, snails) eat mainly plants
- carnivores (e.g. sharks, hawks, spiders, snakes) eat other animals
- omnivores (e.g. cockroaches, bears, raccoons, humans) eat animals and plants
54
Digestive systems
- remember animals get oxygen from gas exchange but for life, animals still need to get food
- animals acquire the food (nutrients) through the digestive system
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Getting and using food
Ingest
- taking in food
Digest
- mechanical digestion - breaking up food into smaller pieces
- chemical digestion - breaking down food into molecules small enough to be absorbed into cells. This involves chemical reactions and requires enzymes
Absorb
- absorb nutrients across cell membranes by diffusion and active transport
Elimination or egestion
- undigested material passes out of body
56
Digestion
- important to understand the difference between mechanical and chemcial digestion
- mechanical digestion - breaking up food into smaller pieces e.g. chewing the food
- chemical digestion - breaking down food into molecules small enough to be absorbed into cells. This involves chemical reactions and recruiters enzymes
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Different digestive systems
- different diets means different structures are needed in the digestive system
- main differences occur in the -
- teeth
- length of digestive system
- number and size of digestive organs
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Teeth
Carnivore
- sharp ripping teeth
- large canines
Herbivore
- wide grinding teeth
- large molars
Omnivores
- both kinds of teeth
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Length of digestive system
Herbivores
- long digestive systems
- harder to digest cellulose (cell walls of plants)
- bacteria needed in intestines
Carnivores
- short digestive systems
- protein easier to digest than cellulose
60
Different stomachs - ruminant
- ruminant stomach are found in sheep, cows and goats. Are called cud-chewing mammals
- cud chewing means they chew their food twice
- their stomach occupied 3/4 of the abdominal cavity. Broken up into four parts -
— rumen
— reticulum
— omasum
— abomasum which is the “true” stomach
- when a cow first takes a bite, it chews just enough to moisten the food
- once swallowed, the food goes into the first section the reticulum, where it mixes with other acidic digestive liquids and is softened. The softened food is called cud, small balls of food
- next, the muscles send the cud back up to the cows mouth, where it is re-chewed and swallowed again. This time going to the rumen and omasum of stomach in order to squeeze out all of the moisture
- finally, the food enters the last part, abomasum of the stomach, where it mixes with digestive juices and make its way to the intestine to be completed digested
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Different intestines - hind gut fermenters
- different intestines are found in animals that eat large amounts of roughages (plant cellulose) but do not have ruminant stomachs
- called hind-gut fermenters, they can utilise large amounts of roughages because of its greatly enlarged caesium (appendix) and large intestine
- such an animal often re-ingest their own faeces to get all the nutrients from the food
- examples are horses, rabbits, Guinea pigs, and hamsters
62
Birds - unique system
- this system differs greatly from any other type
- since a bird has no teeth, no chewing is involved
- the oesophagus emptied directly into the crop. The crop is where the food is stored and soaked to make it wet
- two parts of the stomach -
— proventriculus: same as a single stomach and provides digestive excretions
— gizzard: located after proventriculus, very muscular, used to grind food
- from the crop, the old makes its way to the gizzard. The gizzard is a very muscular organ, which normally contains stones or grit that grinds the food
- digestion in the avian system is very rapid
63
Birds - unique system
- this system differs greatly from any other type
- since a bird has no teeth, no chewing is involved
- the oesophagus emptied directly into the crop. The crop is where the food is stored and soaked to make it wet
- two parts of the stomach -
— proventriculus: same as a single stomach and provides digestive excretions
— gizzard: located after proventriculus, very muscular, used to grind food
- from the crop, the old makes its way to the gizzard. The gizzard is a very muscular organ, which normally contains stones or grit that grinds the food
- digestion in the avian system is very rapid
64
Surface area - key feature of digestive systems
- because acquiring nutrients requires substances to move across the cell membrane (either into the whole unicellular organism or from the digestive system into the rest of the organism) a key feature is that there must be a large surface area
- all systems have features to increase the surface area of the sites where absorption occurs
65
Excretory system - main functions
- filtration of blood
- reabsorption of water and solutes
- secretion of urine
66
Excretory systems
- excretion is the removal of nitrogen-related or other metabolic wastes
- kidneys filter water and solutes from blood. Most of this is reabsorbed back into blood, but the excess leaves the kidneys as urine
- the body adjusts for excess water intake by increasing urine output. Conversely, it adjusts for increased exercise or decreased water intake by reducing urine output
- the kidneys not only prevent the build-up of wastes but also help maintain water balance by controlling the volume, composition and pressure of body fluids
- once of the kidneys have finished filtering and reabsorbing, the resulting urine volume and concentration has been adjusted to enable then balance of water and removal of watses
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Removing carbon dioxide
- humans have lungs
- insects can remove carbon dioxide through trachea and spiracles
- amphibians can release carbon dioixde through their skin and lungs
- aquatic animals rely on diffusion across gills to remove carbon dioxide from the system
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Removing salts
- salt dissociate into ions. Ions such as Na+ and Cl- are required for normal activity of muscles and neurons
- regulation of salt concentration is important in maintains water balance
- salts can be excreted through the kidneys in mammals, or diffusion in other animals
- humans can also remove salts through sweat
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Removing nitrogenous wastes
- there are three different types of nitrogenous waste:
- ammonia, urea no uric acid
- ammonia (NH3) is a waste product formed when proteins are broken down. It is a toxic nitrogen-containing compound
- in mammals, ammonia is converted to urea and is excreted in urine
- in humans, the liver breaks down ammonia into urea, which is carried to the kidneys
- most aquatic animals with little water need,p to conserve water so produce a pasty white uric acid
- nitrogenous wastes come from the breakdown of proteins. They occur in three biological forms:
- ammonia - most toxic
- urea - intermediate toxicity
- uric acid - least toxic
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Specialised mechanisms for excretion
Terrestrial animals such as insects and mammals require specialised mechanisms to remove metabolic waste
- insects use malpighian tubules - pair/pairs of tubes that extend from the digestive system. The tubes remove the nitrogenous waste as uric acid
- mammals use kidneys to remove nitrogenous wastes as urea
71
Excretory systems - mammals
- the nephron is the basic functional unit of the kidney
- each kidney consists of approximately one million nephrons
- water and solutes are filtered at the start of the nephron
- during he journey through the nephron, different amounts of solutes and water are reabsorbed back into the bloodstream
- the amount reabsorbed is determined by the needs of the body
- nephron structures related to to their function
- mammalian nephrons collect urea, unwanted solutes and water forming urine at the end of the structure
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Osmoregulation
Kidneys regulate water balance
Mechanisms to reduce water loss include:
- reptiles and birds reabsorbed water from the cloaca, the cavity into which their ureter and rectum open
- terrestrial vertebrates can slow the production of urine by reducing the glomerular filtration rate
- the Australian desert frog can also swell and store its urine for use in the dry season
- having longer loops of Henle allow organisms to concentrate their urine
- the desert hopping mouse Notomys Alexis can concentrate its urine more than any other known rodent
- camels can tolerate water loss and concentration of their body’s fluids
- the functional unit of the kidney is the nephron
- in the glomerulus, blood plasma is filtered from fine capillaries
- filtrate is collected in the bowman’s capsule
- filtrate travels through the loop of Henle, along with nutrients and proteins are reabsorbed back into the bloodstream
The kidneys:
1. remove nitrogenous wastes from the body
2. Regulate water concentration in the blood
3. Maintain ion levels in the blood
73
Gas exchange
- process whereby oxygen moves from the lungs to the bloodstream. At the same time carbon dioxide passed form the blood to the lungs. This happens in the lungs between the alveoli and the surrounding capillary network
74
Cellular respiration
- is a series of chemical reactions that occur within cells that break down glucose to produce ATP, which may be used as energy to power many reactions within the cell. There are three main steps in cellular respiration: glycolysis, citric acid cycle, and the electron transport chain
75
The source of oxygen
- air is about 21% oxygen (thinner at higher altitudes)
- it is easy to ventilate
- the amount of oxygen in water varies but is always much less than air and even lower in warmer water
- it is harder to ventilate oxygen from water
76
Gas exchange surfaces
Gases move by diffusion
Diffusion is greater when:
- the surface area is large
- the distance travelled is small
- the concentration gradient is high
Gas exchange surface must be moist
O2 and CO2 must be dissolved in water to diffuse across a membrane
Therefore, an efficient gas exchange surface will
- have a large surface area
- provide a small distance for gases to diffuse across
- be moist
- be organised or operate in a way that maintains a high concentration gradient (high to low) for the diffusion of both O2 and. CO2 gases
The surface an organism depends on:
- the size of the organism
- where is t lives - water or land
- the metabolic demands on the organism - high, moderate or low
77
Types of gas exchange surfaces
The four main types of gas exchange surfaces we will look at are:
- through skin
- gills
- lungs
- trachea
78
Gas exchange - simple diffusion
- animals with small bodies exchange respiratory gases sufficiently through the body surface without specilaised respiratory membranes
- protists use direct diffusion into the cell to exchange gases
- although most amphibians have legs they can also perform gas exchange directly through their highly vascularised skin. This means that their skin has lots of blood vessels going through it. Since the blood vessels are close to their permeable skin surface, diffusion can take place right through the skin
- larger animals require a large specialised surface for gas exchange and have a more complex respiratory system
79
Gas exchange in water
Gas exchange in water has
- no problem in keeping the cell membranes of the gas exchange surface moist
BUT
- O2 concentrations in water are low, especially in warmer water and/or saltier water
SO
- the gas exchange system must be very efficient to obtain enough oxygen for respiration
80
gas exchange in water - gills
- gas exchange in water requires gills
- gills covered by an operculum (flap)
- fish ventilate their gills by an alternately opening and closing mouth and operculum
-- water flows into mouth
-- over the gills
-- out under the operculum
- in fish, each gill is made of four bony gill arches
- gill arches are lined with hundreds of gil filaments that are very thin and flat
- gill filaments have folds, called lamellar that contain a network of capillaries
- blood flows through the blood capillaries in the opposite direction to the flow of water
- the gill arch contains an artery that brings deoxygenated blood to the gill and each gill plate is well supplied by capillaries that branch from this artery
- as the water flowing over the gill has a higher concentration of O2 and a lower concentration of CO2, O2 diffuses into the blood capillaries and CO2 diffuses out
- the oxygenated blood is carried away from the gill and excess CO2 is washed away from the gill by the incoming water
gills are efficient gas exchange surfaces because they:
- have a very large surface area created by the folding
- are thin-walled and in close contact with water to create short distances for diffusion
- have a very high blood supply to bring CO2 and carry out O2
- steep high concentration gradient
- are moist: found in animals that live in water
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gas exchange in air
for gas exchange, air has many advantages over water
- air has a much higher oxygen concentration than water
- diffusion occurs more quickly so less ventilation of the surface is needed
- less energy is needed to move air through the respiratory system than water
BUT
- as the gas exchange surface must be moist, in terrestrial animals water is continuously lost from the gas exchange surface by evaporation
SO
- the gas exchange surface is folded into the body to reduce water loss
- land animals (terrestrial animals) must get the oxygen from the air
- many terrestrial animals have lungs
- insects have a system known as the trachea
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gas exchange in air - mammalian lungs
- movement of the diaphragm causes the lungs to be ventilated for gas exchange
- mammalian lungs have a system of tubes (held open by rings of cartilage) that allow air to flow in and out of the lungs
- air enters via the trachea (windpipe)
- trachea branches into two bronchi (one bronchus to each lung)
- bronchi branch into bronchioles
- many alveoli at the end of the bronchioles
- alveoli walls are made of flat cells which are only one cell thick
- each alveolus is lined with moisture
- surrounded by capillary network carrying blood
- air flows into and out of the lungs because of the changes in the air pressure inside the lungs
- expansion of the lungs increases their volume and thus decreases the intrapulmonary pressure
-- air from outside the lungs rushes in in response to the pressure gradient
- when lung volume reduces during expiration, intrapulmonary pressure increases and air moves out through the mouth and nose
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inspiration - breathing in
- during quiet breathing (at rest) inspiration is achieved by increasing the space (and therefore decreasing the pressure) inside the lungs
- air then flows into the lungs in response to decreased pressure inside the lungs
- inspiration is always an active process involving muscle contraction
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expiration - breathing out
- during quiet breathing, expiration is achieved passively by decreasing the space (and thus increasing the pressure) inside the lungs
- air then flows passively out of the lungs to equalize with the air pressure
- in active breathing, muscle contraction is involved in bringing about both inspiration and expiration
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gas exchange in air - insect trachea
- insects have a completely different system
- air tubules (trachea and tracheoles) throughout the body which open to the environment via spiracles
- trachea kept open by circular bands of chitin
- branch to form tracheoles that reach every cell
- ends of the tracheoles are moist
- oxygen delivered directly to respiring cells - insect blood does not carry oxygen
- tracheal system is an efficient method of gas exchange as:
- oxygen is delivered directly to expiring cells
- can pump blood to move air around in tracheal system
BUT
- size of animal is limited by relatively slow diffusion rate (reason why insects are so small)
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gas exchange in air - bird lungs
- birds have a high demand for oxygen:
-- they're warm-blooded so metabolism is high
-- flight requires a lot of energy
- additional challenge:
-- air at higher altitudes is thinner - lower in O2
- some birds can still fly as high, e.g. over mt Everest
- birds have a very efficient gas exchange system to cope with low O2 supply and high O2 demand
- birds have lungs and air sacs
- air sacs are not sites of gas exchange
- air sacs enable a one-way flow of air through the lungs
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passage of air through lungs - birds
- the main air tubes through lungs are the parabronchi
- tiny air capillaries run alongside air capillaries
- the blood flows in opposite direction to air flow to create a counter-current exchange of gases, this maintains the concentration gradient
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features enhancing the efficiency of bird lungs are:
- large surface area
- many tiny air capillaries
- short distance for diffusion as the air and blood capillary walls made of flattened, thin cells and air and blood capillaries alongside each other
- moist as the lining of air capillaries is wet and the system is internal to conserve moisture
- maintaining a concentration gradient as air flows in one direction though lungs regardless of whether the bird is inhaling or exhaling. The one way passage in both parabronchi and air capillaries; other way in blood capillaries creates the counter-current exchange
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transport system
- we need a system which can pick up and deliver the supplies to all the cells. The system also needs to be able to transport all the wastes from the cells to get expelled
- this transport system is the circulatory system
- the circulatory system is also important for other functions such as maintenance of body temperature, the immune response and hormonal control of bodily functions
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simple organisms
- when your body is only two-cell layers thick, you can get supplies in and waste out just through diffusion
- flatworms - every cell is able to obtain nutrients, water and oxygen without the need of a transport system
- the flatworm's flattened body shape also restricts the distance of any cell from the digestive system or the exterior of the organism. oxygen can diffuse from the surrounding water into the cells, and carbon dioxide can diffuse out
- some animals, such as jellyfish have more extensive branching from their gastrovascular cavity (which functions as both a place of digestive and a form of circulation). This branching allows for bodily fluids to reach the outer layers, since the digestive begins in the inner layers
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complex organisms
- complex organisms need a circulatory system to deliver the materials where they are needed
- the main system all complex animals have is called the cardiovascular system
- the cardiovascular system is made up of three parts
-- heart
-- blood vessels which includes
arteries
capillaries
veins
-- blood
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cardiovascular systems
animals cardiovascular systems have a:
- a muscular pump = heart
- tubes = blood vessels
- circulatory fluid = blood
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types of cardiovascular systems
- in animals these are classified as either open or closed systems
- closed circulatory systems have the blood enclosed at all times within vessels of different sizes and wall thickness. In this type of system, blood is pumped by a heart through vessels, and does not normally fill body cavities
- open circulatory systems pump blood into the haemocoel (main body cavity of invertebrates) with the blood diffusing back to the circulatory system between cells. Blood is pumped by a heart into the body cavities, where tissues are surrounded by the blood
- insects have a cavity that is full of insect blood (known as haemolymph) and the organs of the insect are suspended in this cavity.
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open circulatory system
- found in invertebrates (insect, arthropods, molluscs)
structure:
- blood does not remain enclosed in the blood vessels and comes in direct contact with other body cells and bathes them
- there are no typical arteries, veins and capillaries and for much of the time the blood called haemolymph surrounds the cells
- this system does not transport gases like oxygen and carbon dioxide
advantages of an open system:
- requires less energy expenditure to operate
-- can serve other functions. For example, in molluscs the open circulatory system functions as a hydrostatic skeleton in supporting the body
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closed circulatory system
Food in invertebrates such as earthworms, squid, octopuses and all vertebrates
Structure:
- blood always remains in the blood vessels and does not come in direct contact with other cells of the body. Blood confines to vessels and separate from tissue fluid
- one of more hearts to pump blood
- interconnected system of arteries, veins and capillaries present
- exchange of nutrients and waste products between the blood and tissue via tissue fluid occurs at the capillaries
- the system also transports gases, i.e. oxygen and carbon dioixide
advantages:
- closed systems with their higher blood pressure, are more effective at transporting circulatory fluids to meet the high metabolic demands of the tissues and cells of larger and more active animals
- allows animals to control blood flow to different organs as necessary
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vertebrate cardiovascular system
- vertebrates have a chambered heart
-- atrium, which received blood
-- ventricle which pumps blood out
- in vertebrates the number of chambers differs, some only have two, some three, and some four
- a powerful four-chambered heart was an essential adaptations in support of life of mammals and birds. Endothermic use about ten times as much energy as equal - sized ectotherms. Therefore, their circulatory systems need to deliver about ten times as much fuel and O2 to their tissues (and remove ten times as much CO2 and other other wates)
- this large traffic of substances is made possible by separate and independent systematic (body) and pulmonary (lung) circulations and by large, powerful hearts that pump the necessary volume of blood
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heart valves
- there are four valves in the heart. these are flaps of connective tissue which prevent the backflow of blood
- atrioventricular (AV) valve
-- between atrium and ventricles
-- keeps blood from flowing back into atria when ventricles contract
- semilunar valves
-- between ventricle and arteries
-- prevent back flow from arteries into ventricles while there are relaxing
- the heart sounds heard with a stethoscope are caused by the closing of the valves, (even without a stethoscope, you can hear these sounds by pressing your ear tightly against the chest of a friend - a close friend)
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blood vessels
- blood vessels
-- arteries = carry blood away from heart. smaller arteries are called arterioles
-- veins = return blood to heart. smaller veins are called venules
-- capillaries = deliver blood to cells and connect arteries and veins
- arteries, veins and capillaries are the three main kinds of blood vessels, which in the human body have a total length of about 100, 000km
- all arteries carry blood from the heart towards capillaries, and veins return blood to the heart from capillaries. one exception is the hepatic portal vein that carries blood from capillaries bed in the digestive system to capillary beds in the liver. Blood flowing from the liver passes into hepatic vein, which conducts blood to the heart
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blood
- the average 70kg human has about 5L of blood
- approximately 55% of the blood is liquid, called the plasma; remaining 45% is composed of blood cells, including erythrocytes (red blood cells), leukocytes (white blood cells) and platelets
- the blood cells are considered to be a tissue because they are cells that work together for a common cause
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mammalian circulation
- the heart, blood vessels and blood all work together to circulate the required materials around the body
- these are two circulation loops - one pulmonary to the lungs and one systematic to the rest of the body
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steps in mammalian circulation
1. deoxygenated blood enters the right atrium, via the vena cava, from the systematic loop (coming from the body system) of blood and passes into the right ventricle
2. right atrium contracts and pumps blood into right ventricle
3. when the right ventricle contracts, blood is forced into the pulmonary artery, which leads to the lungs (pulmonary loop). This is called pulmonary circulation
4. In the lungs, oxygen diffuses into the blood and carbon dioxide passes out into the air in the lungs
5. the now oxygen-rich or oxygenated blood passes back into the heart via the pulmonary veins and into the left atrium
6. the left atrium contracts and pumps back into the left ventricle
7. when this ventricle contracts, the blood is forced into the aorta, the largest artery, which, through its branches, takes blood to all parts of the body. This is called systematic circulation
- the blood is kept flowering in one direction in the heart by the presence of four valves
- the two ventricles contract at the same time and the atria contract at the same time, but the ventricles and atria contract at different times
- the septum keeps the deoxygenated blood on the right side of the heart from mixing with the oxygenated blood in the left side
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cardiac cycle
- one complete sequence of pumping of the heart is called the cardiac cycle
-- heart contracts and pumps
-- heart relaxes and chambers fill
- contraction phase is called systole
- relaxation phase is called diastole
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blood delivery - aorta
- oxygenated blood leaving the heart in the aorta is sent to all parts of the body
- the aorta divides and branches off into numerous smaller arteries and arterioles
- eventually all the branches delivery blood to every body cell at the capillary level
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exchange in capillaries
- once the blood has reached the capillaries, fluid leaks from capillaries through small gaps where cells join
- the fluid (called tissue fluid) bathes the tissues supplying nutrients and oxygen
- no cell is more than 25μm away from a capillary
- capillary walls are thin enough to allow the exchanges of materials between tissue and blood cells to take place
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returning blood - vena cava
- upon leaving the capillary beds, blood now travelling in the veins makes its way back to the heart
- venules and veins ultimately combine to form the largest vein in the body - the vena cava
- the vena cava empties blood back into the heart at the right atrium
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vertebrate systems
all vertebrate systems have a closed circulatory system
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fish circulatory systems
- fish have a single circuit for blood flow and a two-chambered heart that has only a single atrium and a single ventricle
- the atrium collects blood that has returned from the body, while the ventricle pumps the blood to the gills where gas exchange occurs and the blood is de-oxygenated; this is called gill circulation
- the blood then continues through the rest of the body before arriving back at the atrium; this is called systematic circulation
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amphibians and reptile systems
- in amphibians reptiles, birds, and mammals, blood flow all have the two-loop pattern (double) of circulation
- amphibians have a three chambered heart that has two atria and one ventricle. The two atria receive blood from the two different circuits (the lungs and the systems). There is some mixing of the blood in the hearts ventricle, which reduced the efficiency of oxygenation. The mixing is reduced by a ridge within the ventricle that diverts oxygen-rich blood through systematic circulatory system and deoxygenated blood to the pulmocutaneous circuit
- most reptiles also have a three-chambered heart similar to the amphibian heart that directs blood to the pulmonary and systematic circuits. Then ventricle is divided more effectively by a partial septum, which results (alligators and crocodiles) are the most primitive animals to exhibit a four chambered heart
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crocodile circulation
- crocodilians have a unique circulatory mechnaism where the heart shunts blood from the lungs toward the stomach and other organs during long periods of submergence for instance, while the animal waits for prey
- one adaptation includes two main arteries that leave the same part of the heart: one takes blood to the lungs and the other provides an alternative route to the stomach and other parts of the body
- two other adaptations include a hole in the heart between the two ventricles, called the foremen of pinazza, which allows blood to move from one side of the heart to the other, and specialised connective tissue that slows the blood flow to the lungs
- together, these adaptations have made crocodiles and alligators one of the most successfully-evolved animal groups on earth
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