CCEA AS2 BIOLOGY 2.1

What is meant by surface area

The total number of cells in direct contact with the surrounding environment

What is meant by volume?

Total 3D space occupied by metabolically active tissues

Surface area to volume ratio in large animals

Small surface area to volume ratio

Surface area to volume ratio in small animals

Large surface area to volume ratio

What does volume influence

The demand for metabolites

What does surface area affect

affects the rate of exchange of materials at exchange surfaces

What does surface area influence?

the rate of supply to metabolically active tissues

Organisms size affecting surface area

as an organism's size increases, its surface area increases less than its volume

Large surface area

Methods of increasing surface area

Increasing the amount of the cell in contact with the substance, e.g flattening the cells in the exchange surface

Organisms such as flatworm do this

Larger organisms in increasing surf area

The cells that make up their exchange surf area flattened

e.g. squamous epithelium cells

Thin exchange surfaces

One cell thick so gases only have to diffuse across two layers, maximises the rate of transport

large concentration gradient

A large concentration gradient increases the rate of diffusion,

Breathing helps maintain the gradient in the mammalian lungs

What is mass transport?

The movement of substances from a region of high pressure to a region of low pressure

mass transport in mammals

Circulation- High pressure is created by contractions of the heart, allows blood to move to the lower pressure of cells in the body

Ventilation- An increase in volume in the thorax causes pressure to decrease and air moves into the thorax

mass transport in plants

Xylem- water evaporates from stomata (negative pressure) which causes the water to be drawn up in xylem vessels

Phloem- Sugars moved into the phloem sieve tubes creating HIGH pressure which facilitates movement of sugars to areas with lower pressure (translocation)

Features of a gas exchange surface

Large surface area

Moist surface (dissolving gases)

Diffusion gradients for O2 and CO2

Must be permeable to O2 and CO2

Short diffusion path

Ficks law

Diffusion rate = Surface area x Difference in concentration

/ thickness

Gas exchange in the mammal is in the

Alveolar wall (Alveoli)

Large surface area in alveoli

700 million alveoli

350 mil in each lung

SPHERICAL shape

Contact surf area between alveoli and blood is maximised by the proliferation of capillaries

Thin surfaces in alveoli

Thin surfaces give a short diffusion path

Lined by squamous epithelial cells (0.2 nanometres thick)

Alveoli surrounded by capillaries with an endothelial lining consisting of a single layer of squamous epithelial cells

Steep concentration gradient in alveoli

Caused by ventilation of lungs e.g o2 in and co2 out

Flow of blood through capillaries maintains gradient as it continually brings CO2 rich blood into the alveoli and removes O2 rich blood from alveoli.

Moist surfaces in alveoli

Outer surface is moist

Surfactant in the moisture layer to reduce surface tension

Inspiration in Mammals (Breathing in)

External Intercostal muscles contract

Ribs pull upward and outwards

Diaphragm contracts and flattens from its dome shape

These actions increase the volume of thorax and decrease pressure around the lungs

Expiration in mammals (breathing out)

External intercostal muscles relax

Ribs move downwards and inwards

Diaphragm relax and returns to domed position

Decreased volume of thorax

Increased pressure in lungs

Higher pressure than atmosphere so air is forced out the lungs

Respiration

Produces energy, takes place all the time

Photosynthesis

Produces carbohydrates requiring light energy and occuring during daytime

Plants at night

Carry out respiration only

Plants at daytime

Plants carry out respiration AND photosynthesis

Light levels affecting respiration and p/s

High light levels- P/S is higher than resp

Low light levels- P/S and resp are the same (compensation point)

Compensation point

The rate of CO2 used in photosynthesis is the same as the rate of CO2 produced in respiration

Where does gas exchange occur in plants?

Cell surface membrane of the spongy mesophyll cells

Adaptions of the leaf for gas exchange

Thin leaves- (High SA/V ratio) and short diffusion distance

Gas exchange surfaces of spongey mesophyll cells are LARGE and MOIST

Loose arrangement gives large surf area for gases to diffuse

Large intercellular air spaces in spongy mesophyll FACILITATE DIFFUSION

Stomata

Pores in leaf surface that allow respiratory gases to diffuse in and out of the leaf

Stomata at daytime and night

Stomata open at daytime and close at night

Open at day as diffusion of gases is greatest

Closed at night to ensure water loss is reduced

Stomata is controlled by

The guard cells which change their shape

Smoking can cause..

Cilia, Lung cancer, Bronchitis, Emphysema

Respiratory tree

Epidermis

Outer layer of a root

The vascular tissue core in a central stele

Endodermis

Single layer of cells outside the central stele

Water proof layer formed of suberin called the Casparian strip.

Cortex

A layer of undifferentiated cells

Xylem

Adapted to water transport by

-No end walls

-No cell contents

-Dead when formed

-Walls thickened with lignin

Lignin adaptions in the xylem

Protoxylem- Found in the elongation behidn the root tip and has annular and spiral thickening

Doesn't restrict elongation of the xylem vessels as growth of root tips take place

Metaxylem

- Reticulate or pitted pattern (Complete covering of lignin)

Pitted patterns have small pits which allow the movement of water between adjacent cells

Phloem

Have sieve tube elements for transport (for sugars and amino acids)

What are sieve tube elements?

They are living cells with cell contents

Sieve tube elements have end walls and are perforated with sive pores to form sieve plates

They have NO nuclei when fully grown

Sieve tube elements contents

Microtubules that pass through the sieve pores

Each have a companion cell

Companion cells are rich in mitochondria and dense cytoplasm

Companion cells carry out metabolic activities for the sieve tube elements

Properties of Lignin

Great strength, prevents vessels from collapsing when under pressure.

Waterproof, prevents the leakage of water

Vascular tissue in stem

Arranged as VASCULAR BUNDLES which provides greater support

1 ) Transport of water into and across the root

Water enters root hair cells by osmosis

Water in the soil has a higher water potential than the root hair cells so water moves into the root hair cells along a water potential gradient

Ion uptake is carried out by

Active transport

The apoplast pathway

Involves water moving along the cellulose microfibrils of cell walls

Microfibrils has parallel arrangement with allows water to pass between the diff players easily

Mesh-like structure arrangement of walls aids movement

Cohesive properties of water help pull the water column along

The symplast pathway

Involves water moving by osmosis from cell to cell across the cortex

Movement of water across the root creates a water potential gradient necessary for osmosis to take place

Water moves from cell to cell through the plasmodesmata that link the cells of the cortex together

What does the Casparian strip do (Endodermis)

Prevents water moving through the endodermis

Protoplast in pathways

Water moving through the apoplast pathway moves into the protoplast to join water moving in the symplast pathway

All water moving into the stele is transported by the symplast and ensures the water transport is under METABOLIC CONTROL

Water up the plant

Endodermal cells - Pump ions into the xylem cells

Creates a water potential gradient

Movement of water by osmosis into the xylem tissue creates a root pressure force that helps water move up the plant

2) Transport of water up the root and stem into the xylem

Water evaporates out of the stomata and creates a negative pressure, pulls the water column up the xylem

Water column forms a continuous unbroken pathway

Water molecules form H bonds with eachother (cohesion) which sticks the water molecules together

Cohesive properties of water

Cohesive properties allows water to be sucked up the xylem in a continous column, water at the leading edge of the column evaporates out of the leaf

Cohesion tension theory

1) If the water column in the xylem is broken, an air gap appears and water below gap cant be pulled up

e.g. the time between buying flowers and placing them in the vase of water, air will enter the bottom of the cut stems.

Placing them in water after will make no difference as the column is broken.

Adhesion / Adhesive properties of water

Adhesion is when water molecules cling to the walls of the xylem and help pull up water

Adhesive forces between the water column and the xylem reduce the forces necessary for transpiration pull

3) Transport of water through the leaf and the evaporation of water from the leaf

- Water enters leaf in midrib, midrib splits into a number of veins that distribute water across leaf.

-Water passes from the vein to surrounding cells, some is used in P/S or providing turguor but most is lost in transpiration

What is transpiration?

The evaporation from water from the mesophyll surface, followed by diffusion of water vapour through the stomata and into the atmosphere.

How do transpirational losses occur

Due to water evaporating of cell surface membranes of the spongey mesophyll and water vapour diffusing down the conc gradient out stomata.

Transpiration sets up a water potential gradient that's responsible for transpiration pull

Water trasport from xylem into..

Spongy mesophyll cells through apoloplast and symplast pathways

Factors affecting the rate of transpiration (INTERNAL)

1) Stomatal density- Refers to the no of stomata in leaf. The more stomata per unit area in leaf more transpiration

2) Leaf surface area

The greater the leaf surface area, more transpiration

3) Cuticle thickness

Thicker cuticles tend to loss less water by evaporation

External factors affecting transpiration

1) Light intensity- Evaporation and transpiration greater during the day, at night stomata is closed.

2) Wind speed

Increases the rate of evaporation

Wind removes diffusion shells by blowing humid air away

This maintains a steep water potential gradient allowing water to evaporate rapidly from the spongy mesophyll

3) Temperature

The higher temperature. the faster rate of evaporation of water from spongy mesophyll cells

4) Humidity

Increasing humidity decreases the rate of evaporation adn transportaion

Humid air decreases water potential gradients

Sub stomatal air aspaces become more humid due to the build up of water vapour which decreases evaporation.

5) Soil water availability

During dry summers evaporation and transportation rates can be lower due to lack of water in the soil

IF a plant is dehydrated the stomata will close (defense mechanism to conserve water)

Xerophytes and their adaptions

Xerophytes are plants that are highly adapted to reduce water loss by transpiration

1) Leaf curvature

Lower epidermis is enclosed and protected, this folding creatres a layer of humid air within the leaf.

Which significantly reduces the water potential gradient between the inside and outside of the leaf.

2) Reduced surf area

Leaves reduced to spines/needles e.g. in cacti

Reduction in surface area reduces the area which transpiration can take place

3) Cuticular thickening

Thick cuticle makes this waterproofed layer efficient in reducing evaporation

4) Succulent tissue

Succulent (juicy) leaves store large quantities of water which can be used in periods of drought.

5) Leaf hairs

Restrict air flow and trap layers of humid air.

Reduces water potential gradient in inside and outside of leaf

6) Sunken stomatas

Stomata are sunk in pits, reducting transpiration loses by creating layers of humid air around it.

Layers of humid air called diffusion shells which reduces the water potential gradient.

7) Shallow roots

Roots that cover a wide area and ensures rain water can be quickly absorbed before it gets a chance to evaporate

Hydrophytes

Plants that are adapted for living in water (Water lilies)

Adaptions of hydrophytes

Stomata being restricted to the upper surface --->

Prevents stomata from being submerged in water allowing gas exchange to take place

Large air spaces that enables the plant to float. (Aerenchyma)

Translocation of organic solutes through the phloem

Translocation is the movement of organic substances through the phloem

The phloem trasnports organic substances from the leaves to carbs (energy) amino acids (growth) and to the roots for storage

The main substance transported in the phloem is..

the disaccharide sucrose

Evidence for Energy expenditure in t he phloem

Companion cells have rates of metabolic activity.

Closely associated with sieve tube elements and energy output is linked to the processes that take place in sieve tubes

Companion cells in phloem are involved in uptake of sucrose from photosynthesizing cells and then loading sucrose in the ST elements

Metabolic inhibitors

such as cyanide stop respiration in plant cells

Evidence for two way transport of sucrose

Radioactively labelled sucrose (from carbon 14), which sows that sucrose can move up and down the stem

Circulatory system in mammals

Double circulatory system- Blood goes through heart twice for each complete circuit of body

Blood flows through 2 circuits which are called

The pulmonary circuit (right side of heart)

The systematic circuit (left side of heart)

Pulmonary circuit

Pumped at low pressure, blood passes slowly through capillaries which allows more time for gas exchange

Systematic circuit

Pumped at a high pressure which allows the transport of metabolites

Arteries

Carry blood away from heart

- Fibrous outer layer

- Thick middle layer of smooth muscle

- Inner layer of squamous endothelium cells

- Narrow lumen

- Rounded shape

- High blood pressure

Arteries contain tissue called

Elastic tissue allows artery to stretch and recoil, helps blood push along the artery maintaining blood pressure

The muscle tissue/fibres provide support but can also constrict vasoconstriction or dilate vasodilation

Veins

Also consists of a outer layer of fibrous tissue with a THIN middle layer of muscle, contains squamous endothelium

-Thin wall

-Large Lumen

-Valves (to prevent backflow of blood)

-Irregular shape

Veins adaptions

Large lumen does not resist blood flow

Valves prevent backflow

Endothelial layer of squamous gives a smooth surface (reduces friction)

Fibrous layer for protection

The vein has a large lumen to

faciltate the return of blood back to heart

Capillaries

ONE cell thick walls (composed of squamous endothelium)

Extensive network gives large surface area for diffusion

Thin and permeable walls providing short diffusion distances

Atrium

Thin walled to receive blood from the lungs

Pumps blood to ventricles

Ventricles

Thick walled to pump blood around the body (left ventricle) and to the lungs (right ventricle)

Right ventricle

Doesn't have to pump blood with too much force because its already close to the heart, too much force damages the pulmonary capillaries