Biology 🧬 Unit 7 - Lessons 1 & 2

the larger the organism the ……. It’s surface area : volume ratio is

Lower

What are 6 features of specialised exchange surfaces

1. Large SA:V ratio (increases rate of exchange)
2. Very thin (short diffusion distance)
3. Partially permeable
4. Movement of the internal medium (eg blood to maintain concentration gradients)
5. Constant movement of the environmental medium (eg. Air to maintain a concentration gradient difference)
6. Moist (in some cases) - allows gases or other materials to dissolve into the water at the exchange surface then diffuse through the surface

plants are autotrophs, what does this mean

They make their own food

Why can single celled organisms rely on simple diffusion to take up their substances

They have a large SA:V

With single-celled organisms the concentration gradients are always maintained as substances are constantly being used up/produced

Diffusion distances are short

Why can’t larger organisms rely of simple diffusion to get their nutrients

SA:V not sufficient to allow for their required exchange of substances/nutrients and for removal of poisonous waste products

Simple diffusion would take too long

Also the more active an organism is the increased need there is for internal transport systems

What are the features of transport systems

* Must have a suitable medium eg. Blood in which to carry materials (normally water based as it’s easy to dissolve things in water)
* A form of mass flow transport in which the transport medium is moved around in bulk over large distances
* A system of tubular vessels that contains the transport medium and forms a branching network
* A mechanism for moving the transport medium within the vessels - requires a pressure difference eg. Heart or natural gradients eg. Evaporation
* A mechanism to ensure mass flow in one direction eg. Valves
* A means of controlling the flow of the transport medium (to suit the changing needs of different parts of the organism

What are herbaceous plants

Plants that have stems that are soft and non-woody

What are dicotyledons

Flowing plants either woody or herbaceous that have developed from seeds that have 2 embryonic leaves, they have a network of veins and in stems their vascular tissue is arranged in bundles and in a ring pattern

What are the 2 factors that determine the need for a pump and the size of an internal transport system

1. SA:V ratio
2. How active an organism is eg. Plants are not very active

What does the term vascular refer to

Tubes or vessels

Which is slower, movement in the vascular bundle or blood in animals

Movement in the vascular bundle is much slower

What are the adaptations of the root hair cells for their function

Long thin projections to increase the surface area of the epidermis to maximise water and mineral ion uptake

Describe the features of the xylem

Vertical rows of dead cells (known as xylem vessel elements)

Long continuous hollow tubes

Transports water and mineral ions from the roots upwards

One directional transport

Walls strengthened by waterproof lignin which withstands tension and allows adhesion to water molecules to support the water column

What strengthens the xylem walls

Walls strengthened by waterproof lignin which withstands tension and allows adhesion to water molecules to support the water column

Describe the role of the phloem

Transports amino acids and sugars up and down the plant (2 directional transport) transports from source tissues to sink tissues

Living cells make up the phloem

What makes up the vascular bundle

Xylem and phloem

What magnification are low power ‘plan’ drawings done on

X10 magnification - not x4!

what magnification should high power drawings be drawn on

X40 magnification

what is the outermost layer of stems and leaves known as

The epidermis

What are the features of parenchyma

Roughly spherical , have large vacuoles and thin-walled cells, making them useful packing tissue

What may parenchyma be used for

1. Storage of foods like starch
2. The cortex of stems and roots and the pith of stems is composed of parenchyma cells
3. When turgid, they help to support the plant, preventing wilting
4. Air spaces between the cells allow gas exchange
5. Water and mineral salts are transported through the walls and through the living contents of the cells
6. Parenchyma forms the cortex in roots and stems and the pith in stems, the cortex is an outer region of cells. The pith is made up of similar cells but is the name given to the central region of stems
7. Parenchyma contains chloroplasts in leaves where the parenchyma cells are modified to form the palisade and spongy mesophyll (so is involved in photosynthesis)

What is collenchyma and where is it normally found

Collenchyma tissue is commonly found as a layer directly beneath the outer epidermis

It is a modified form of parenchyma with extra cellulose deposited at the corners of the cells. This provides extra strength

The midrib of leaves contains collenchyma

What is sclerenchyma and what is it used for

Like xylem vessels they are long, dead empty cells with lignified walls; however they are used for structural function and do not transport water

When living these cells have more lignin than the other cells and are primarily used for support

Sclerenchyma fissure is very important for support and strength in areas that are no longer elongating

At maturity they have no cytoplasm and are considered to be ‘dead’

Sclerenchyma fibres are often associated with the xylem and phloem to help to form the vascular bundle

What are the 3 basic types of plant tissue

Parenchyma tissue

Collenchyma tissue

Sclerenchyma tissue

What is the role of the stem

To support the leaves in obtaining sunlight

To transfer organic substances ions, and water between the different parts of the plant - occurs in the vascular bundles

The xylem is found on the ….. of the stem, and the phloem is on the …….

inside, outside

What is the thin layer of cells between the xylem and phloem called

The cambium

What lies on the outside of the vascular bundles

The cortex

What lies on the inside of the vascular bundles

The pith

What do the cortex and pith consist of

Living and unspecialised cells with thin cell walls

How are lateral forces (caused by wind) best resisted

by an outer layer of supporting tissue

The vascular bundles form a non-continuous ring towards the edge of the stem (gaps between the vascular bundles) - as the ring is non-continuous this ring of supporting tissues allows the stem to bend in the wind

Where does most photosynthesis in the plant occur

In the leaf

What does the leaf consist of

A leaf blade (lamina) connected to the stem by a leaf stalk

How is the leaf blade adapted for it’s function

it is very thin and has a very large SA:V ratio

Within each vein/vascular bundle there is an area of xylem towards the ……. surface of the leaf and an area of the phloem towards the …….. surface

Upper, lower

Describe the features of the epidermis

Upper and lower is a continuous tough transparent, colourless single layer (one cell thick) of cells surrounding the mesophyll tissue that provides protection and allows for diffusion of gases on the underside of leaf

Lower epidermis especially has many tiny pores called stomata

There is also an external waxy cuticle to the epidermis

What is the function of the stomata

Gas exchange takes place through the stomata between the air and the interior of the leaf, each stoma consists of 2 elongated guard cells which can open and close the stomata in response to different environmental factors eg. Temp, wind or sunlight

What is the function of the waxy cuticle

To reduce water loss and helps to protect the organ from drying out and from infection

How is the leaf supported

By a network of vascular bundles throughout the leaf blade and the turgidity of all its cells

What type of specialised cells make up the mesophyll

Parenchyma cells (found between the lower and upper epidermis of the leaf)

The cells of the mesophyll layer are specialised for ……… so they are packed full of ……….

photosynthesis, chloroplasts

What are the two types of mesophyll and what are they the sites for

palisade mesophyll - main site of photosynthesis

Spongy mesophyll - has many large air spaces for efficient diffusion of gases, provides a large SA for gas exchange

There is a thin film of ……. On the surface of mesophyll cells which allow for the dissolving of gases

Water

Gases diffuse from the air into and out of the leaf through many …….. which open and close in response to ……. And ……..

stomata, heat, sunlight

Rate of transpiration will be ……… on hotter days

Higher

Why is the rate of transpiration higher on hotter days

As that is when the difference in concentration gradient will be greatest

What percentage of water is lost through the waxy cuticle

10%

How does an external increase in temperature speed up transpiration

as water molecules will have more kinetic energy and are more likely to evaporate from the surface of the cell wall due to the molecules moving faster

How does an external decrease in humidity speed up transpiration

dry air has a lower water potential than humid air, the greater the water potential gradient between the plant and the air the faster the rate of evaporation

How does an increase in wind speed affect transpiration

the wind moves the moist air away from the stomata thus lowering the water potential of the air increasing the water potential gradient and the rate of evaporation

How does an increase in light effect transpiration rate

stomata are open in the light and closed in the dark to reduce the amount of water loss when the plants need no carbon dioxide for photosynthesis

How does very dry conditions effect transpiration

in especially dry conditions when the water potential gradient between the internal air spaces and the external air is steep a plant may have to compromise by partially or completely closing its stomata to prevent its leaves drying out, even if this means reducing the rate of photosynthesis