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
Q
Transporting from the leaves
A
- 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
Q
Phloem
A
- 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
Q
Phloem structure
A
- 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
Q
Sieve elements
A
- 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
Q
Sieve plates
A
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
Q
Companion cells
A
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
Q
Parenchyma
A
- 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
Q
Waste removal in plants
A
- 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
33
Q
Translocation
A
- is the net movement of sugars in solution through the plant
34
Q
Plants need oxygen too
A
- 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
Q
Gas exchange in plants
A
- 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
Q
Gas exchange in vascular plants
A
- 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
Q
Stomata
A
- 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
Q
Guard cells
A
- 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
Q
Regulating stomata
A
- 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
Q
Why not leave the stomata open
A
- 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
Q
Sensitivity of stomata
A
- 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
Q
Gas movement through the plant
A
- 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
43
Q
Beyond the leaf
A
- 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
Q
Gas exchange in aquatic plants
A
- 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
