Ch 12: Plant Systems for Life

Question 1

What are the two systems in plants?

Answer 1

1. The shoot system is comprised 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.
2. The root system is below ground and is responsible for absorbing water and nutrients from the soil.

Question 2

What are some features of non-vascular plants?

Answer 2

non-vascular plant - plants without a vascular system and with less variety of specialised tissues

• Do not have vascular tissue (do not contain xylem and phloem)
• root-like, stem-like and leaf-like structures.
• found close to water sources
• lack roots, instead root-like structures called rhizoids (small hairs) are elongated cells that attach the plant to the soil
• reproduce by creating single-celled spores or asexually by vegetative propagation
• i.e. mosses, liverworts

Question 3

What are vascular plants and what do their tissues look like?

Answer 3

• have vascular tissue to transport substances in plants
• have xylem, phloem

Question 4

What is xylem tissue?

Answer 4

• responsible for the transport of water, minerals and dissolved nutrients from the roots to the rest of the plant
• made up of 2 types of cells; tracheids and vessel elements. These tissues consist of tubules, elongated cells that allow water to pass freely
• as they mature they die, leaving behind hollow walls supported by the remaining cell walls. These are ideally suited for the transport of water
• the dead xylem tissue forms the woody part of many plant stems, this provides the main support for many large plants i.e. trees

Question 5

What is phloem tissue and what does it look like?

Answer 5

• conductive tissue composed of thin-walled cells that transports sugars and other plant products from where they are produced, often in the leaves, to the rest of the plant
• composed of sieve tube cells and companion cells
• sieve tube cells - long, thin phloem cells that have large pores through the cell walls at either end they have no nuclei, mitochondria or vacuoles, they are arranged end-to-end into sieve tubes sharing cytoplasm, as a result each sieve tube forms a channel through which sugars and other plant products flow
• companion cell are found alongside sieve tubes they have a cell nucleus and other cell organelles. They control the activities of the sieve tube cells. In trees the phloem is the innermost part of the bark

Question 6

What does the functioning plant look like and how are there specific processes to maximise inputs and utlise/remove outputs?

Answer 6

• best position for leaves, photosynthetic organs of the plant, is high above the ground and at the uppermost tip of the plant at the end of the stem, so that there is maximum exposure to sunlight as well as O2 and CO2

Question 7

How is water transported in plants?

Answer 7

Water is absorbed initially by the roots and moves against the pull of gravity through the stem to the leaves via the xylem.

Question 8

What is the function of the root system and how does it transport water?

Answer 8

• absorb water and minerals from the soil, support and anchor the plant and, in many plants they are the main storage tissue
• 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.
• 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, just behind the tip of the root. A plant’s 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 as each root hair is an extension of each root epidermal cell
• the taking up of water through root hairs is faster as it is easier for water from the soil to move into the epidermal cell (6x faster than higher up the root)

Question 9

What are the 2 most common forms of roots?

Answer 9

taproots

• large tapering main root that has only slender short side branches
• able to push vertically through soil to remove water
• found in eucalypts, daisies, orchids

fibrous roots

• many smaller roots of about equal size that grow out from the bottom of the plant stem
• don’t grow deeply but hold the soil in place, preventing erosion
• often used as colonising plants where wind and water erode the sand from the foreshore
• i.e. grasses

Question 10

What is the shoot system?

Answer 10

• the structure of the specialised tissues and their arrangement in the stem makes it possible for water and mineral ions to move upwards, sometimes to great heights. These tissues, along with phloem tissue, are grouped into a series of vascular bundles, each rather like an electric cable in the stem.
• in dicotyledon 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 visible on a leaf are vascular bundles.

Question 11

How is water moved up the stem?

Answer 11

• What makes water up the stem as root pressure is reduced?
  
  • Adhesion: an attractive force between the water molecules and the xylem tube.
• What prevents the water column breaking?
  
  • Cohesion: an attractive intermolecular forces between water molecules keeps a continuous column.
• Therefore, following the reduction of root pressure, the combined forces of adhesion and cohesion ensure the continuous column of water movement (transpiration stream) through the xylem tissue in the stem of the plant.
• the constant upwards movement is driven by transpiration, the evaporation of water from the leaves. Continuous columns of water therefore hang from the top of the plant, from the leaves, down through the xylem, to the roots. The force that holds them there is generated by the sun, evaporating water from the leaf to the atmosphere, and by the forces that act on the water in the stem. This process, where the water is pulled up large vertical distances through the xylem, is called transpirational pull.

Question 12

What does the shoot system look like?

Answer 12

Question 13

What does water movement in a plant look like?

Answer 13

Question 14

What happens when more water is lost through transpiration then is taken up?

Answer 14

water stress - if 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
• water potential gradient between soil & 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.

Question 15

How does gas exchange occur in plants?

Answer 15

The movement of gases in leaves depends on simple diffusion and happens locally over short distances. No transport system is used as they don’t need to be transported from one part of the plant to another

Question 16

How is gas echange efficiency increased by adaptations in the leaves?

Answer 16

• flat and large maximising SA:V
• open air spaces, provide greater SA and allow gases to move freely through much of the leaf without having to pass through cells

Question 17

What is a stomata, where are they found and how do stomata function?

Answer 17

stomata-the openings in leaves and some stems that control the movement of gases into and out of the plant (singular stoma/stomate)

• Numerous stomata are found on the lower epidermis, much more than the upper epidermis.
• Each stomatal pore, or stoma, is bordered by guard cells, a pair of crescent-shaped cells.
• A stoma opens when guard cells absorb water, and closes when they lose water. As a result, stomata tend to be open when a plant is experiencing moist conditions, and closed when a plant is experiencing dry conditions.
• When oxygen or carbon dioxide enters the leaf and arrives at the cell surface, it dissolves in solution on the moist cell membrane. Here it diffuses directly across the cell wall and plasma membrane into the cell.

Question 18

Where is the stomata commonly found?

Answer 18

• Australian eucalypts tend to have leaves which hang vertically and these have many stomata on both surfaces. This helps minimise exposure to the hot midday sun.
• in many broadleaf plants, the stomata are most commonly found on the underside of the leaf
• plants that float on water generally have stomata only on their upper surfaces
• plants that grow under water may have no stomata at all

Question 19

What effects the timing of the opening and closing of stomata?

Answer 19

it depends on a number of environmental conditions

• light as the main factor that initiates opening: in natural conditions, stomata open at daybreak and close at night

other factors can override the effects of light

• temperature: as it increases, water loss exceeds uptake of water so the water content of the plant will fall. Eventually the guard cells will begin to lose their water and the stomata will close
• water availability: photosynthesis may be reduced and the concentration of CO2 will risem this cause the stomata to close and no further CO2 will diffuse in. Conversely, a fall in CO2 concentration can cause the stomata to open
• humidity: if the air is saturated with water vapour, the rate of water loss from leaf cells is reduced, enabling the stomata to stay open. However water is also lost through open stomata as water vapour, if this happens in excess the plant wilts
• severe water stress: i.e. drought, guard cells lose water during the day and close stomata.This reduces water loss but alsocuts CO2 supply. Restricts photosynthesis and reduces overall plant growth.

Question 20

What must plants balance?

Answer 20

Plants need to balance their gaseous requirements with their ability to withstand water loss.

Question 21

How have some plants evolved to store carbon compounds?

Answer 21

this allows them greater control over when and under what conditions they open their stomata. They open their stomata during the evening, when it is cooler and effectively store CO2 for use in photosynthesis in the daytime. They are able to close their stomata during the hottest part of the day

i.e. pinapples, many cactuses, orchids

Question 22

How do plants obtain and transport nutrients?

Answer 22

1. minerals are absorbed by the appropriate ions from the surronding water for aquatic plants and from the soil water in terrestrial plants
2. minerals are actively transported/pumped into the root hairs and other surface cells in the young or growing parts of the root, the ions then move between cells through the plasmodesmata, or junctions between cell
3. one inside the vessels and tracheids (xylem cells), the ions are carried up the stem along with water in the transpiration stream
4. once the mineral ions reach the leaf they are used to produce more chlorophyll, proteins, carbohydrates and other materials

Question 23

What occurs to plants that do not receive sufficient mineral ions?

Answer 23

they suffer from deficiency diseases which can be seen as

• yellowing of leaves
• small leaves, or
• stunted growth

Question 24

What is the distinction between food and nutrients in plants?

Answer 24

food - refers to molecules that are processed through digestion and cellular respiration to provide energy to power cellular processes

nutrients - refers to substances required for the complex chemistry that runs every cell, they do not provide energy, ie.e soluble minerals and salts such as sodium, potassium and phosphorous

Question 25

What is the function of a mycorrhiza and what plants posses it?

Answer 25

• plants that are located in low or lack mineral ions i.e. humus- rich soil and are deficient in mineral ions possess a mycorrhiza
• it is an association between a plant’s roots and a fungus. It is either located on the surface or inside the root
• it has the effect of increasing the area of the root and has the ability to break down the humus into soulble nutrients, some of which are absorbed and used by the plant

Question 26

How does the structure of leaves increase their function efficiency?

Answer 26

• Leaves are perfectly designed to capture light energy, their location and orinetation ensures uninterrupted exposure to the sun
• They are generally thin and flat and collectively present a large surface area to the light - maximising the photosynthesis rate
• Leaf shape is maintained by the turgor of the living cells inside them, the midrib and veins that are well supplied with strengthening tissue.
• The midrib and veins consist of vascular tissue, the xylem and the phloem.

Question 27

How do leaves prevent evaporative water loss?

Answer 27

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.

Question 28

What makes the leaf the best organ suited to photosynthesis?

Answer 28

• its location allows more sunlight to strike its upper epidermis so the more closely packed palisade mesophyll cells absorb the most light energy
• broader leaves offer a larger SA than narrow leaves, they are more efficient at absorbing light and allowing the transfer of water and gases across the membranes
• the stomata allows for the diffusion of CO2 and O2 into and out of cells
• the vascular tissues allow for the transport of minerals and organic compounds throughout the plant
• every leaf cell is close enough to the vascular tissues of the plant to ensure they are adequately supplied with water via osmosis

Question 29

Describe the 2 types of cells that contain chloroplast?

Answer 29

• Those immediately beneath the upper epidermis, called palisade cells, are elongated with their long axes perpendicular to the surface.
• They are separated from each other by narrow air spaces and are densely packed with chloroplasts to maximise light absorption beneath the transparent epidermis.
• The palisade cells collectively form the palisade mesophyll that may be one or several cells thick.
• Between the palisade layer and the lower epidermis are the spongy mesophyll cells.
• Irregular in shape and arrangement.
• Also contain chloroplasts but less than the palisade cells.
• This is why the lower side of a leaf usually looks paler than the upper side.
• If the plant is well supplied with water, the thin cellulose walls of the spongy mesophyll cells are permanently saturated with moisture.
• Between the spongy mesophyll are large air spaces that are linked with each other and with the narrower air spaces between the palisade cells.
• This system allows gases to diffuse freely between the cells within the leaf.

Question 30

How are the products of photosynthesis distributed?

Answer 30

• Translocation is the movement of sugars in solution through the plant.
• Sugars, usually in the form of sucrose are actively transported against a concentration gradient into the sieve cells.
• The energy required for this comes from cellular respiration in mitochondria of companion cells
• Concentration of sugar in the phloem increases, water moves from xylem to sieve cells by osmosis.
• Volume of liquid in sieve cells increases causing syrup (sugar solution) to move to the root, new growth or fruits.
• Sugar leaves the sieve tube cells for the cells where it is needed for cellular respiration, with water following again by somosis
  *

Question 31

What happens when more sugars are produced than can be used by a plant?

Answer 31

many plants form tubers, bulbs or corms. Excess products are transported to these for storage as starch until they are needed. When the next growing season arrives the stored starch is converted into soluble form and transported to the growing points of the new plant.

Unused or stored nutrients can also be translocated out of leaves of deciduous plants before they are dropped in autumn.

Question 32

What is phloem sap?

Answer 32

Phloem sap is mostly a sugar solution; the sugar is sucrose in most species of plants.

Phloem sap may contain up to 30% sucrose by weight, giving it a very syrupy consistency. It is also highly nutritious, which is very attractive to a range of sucking insects that feed on it.

Question 33

How are wastes removed?

Answer 33

• Deciduous plants store wastes in leaves which drop off in autumn.
• Non-deciduous trees remove salt also by leaf fall.
• Plants with bark can transfer unwanted material via the phloem to the bark before shedding.
• Other wastes may be stored as insoluble crystals or dissolved in vacuoles
• Woody plants store wastes in non-living tissue. Cell walls are used as a depository for toxins (lignin).
• Certain plants remove wastes as resins, fats, waxes and complex organic chemicals, like latex from rubber trees.