04. Plant Form and Function Flashcards

Question

What are the features of the collenchyma cells?

Answer 1

• They are generally elongated • They have thicker primary walls than parenchyma cells • Their walls are unevenly thickened • Young stems and petioles often have strands of collenchyma cells just below the epidermis • Even at functional maturity they are living, ﬂexible and elongating with stems and leaves they support

Answer 2

Give mechanical support to leaves and stems without restraining growth

Answer 3

• Secondary cell walls are produced after cell elongation • They have secondary cell walls thickened by large amount of lignin • They are dead cells at maturity

Answer 4

1. sclereids 2. ﬁbers

Answer 5

are shorter and wider than ﬁbers and irregular in shape. They have very thick ligniﬁed secondary cell walls. They are found in places where growth has stopped e.g. nut shells, seed coats and ﬂesh of coarse fruit.

Answer 6

are usually grouped in strands. They are long, slender and tapered. Used commercially to obtain ﬁbers. e.g: coconut husk ﬁber, hemp ﬁbers

Answer 7

They are shorter and wider than ﬁbers and irregular in shape. They have very thick ligniﬁed secondary cell walls. They are found in places where growth has stopped e.g. nut shells, seed coats and ﬂesh of coarse fruit.

Answer 8

are usually grouped in strands. They are long, slender and tapered. Used commercially to obtain ﬁbers. e.g: coconut husk ﬁber, hemp ﬁbers

Answer 9

Sclereids and ﬁbers are specialized to provide support and strength.

Answer 10

• It consists of vessel elements, tracheids, ﬁ bers and parenchyma cells in angiosperms and some of the gymnosperms. • Vessel elements and tracheids mainly conduct water. • They are dead at functional maturity. • Fibers give mechanical strength. • Parenchyma functions in storage and in radial transportation.

Answer 11

• In all angiosperms and some gymnosperms, contain vessel elements • They are cylindrical and long. • They are wider, shorter and have thinner walls than tracheids • Secondary walls are thickened by lignin • They provide support to prevent collapse under tension of water transport • Perforation plates are present at end walls of vessel elements. Other walls are interrupted by pits • They form xylem vessel by aligning end to end with perforation plates • Water ﬂows freely through perforation plates

Answer 12

• Found in all vascular plants • Long, thin cells with tapering ends • Secondary walls are thickened with lignin and often interrupted by pits • Water moves from end to end through pits • Thickening by lignin provides support to prevent collapse under water transport

Answer 13

• It consist of sieve tube elements, companion cells, parenchyma cells and bers in angiosperms • Except ﬁbers other phloem cells are living cells • In seedless vascular plants and gymnosperms sieve tube elements and companion cells are absent. Instead of sieve tube elements, long narrow cells called sieve cells are present in these plants.

Answer 14

In seedless vascular plants and gymnosperms

Answer 15

• Sieve tube elements lack nucleus, ribosomes, a distinct vacuole, and cytoskeletal elements- • cytoplasm reduced into a thin peripheral layer. • Absence of these allow passing of nutrients more freely • Chains of sieve tube elements are aligned to form sieve tubes • The end walls between sieve tube elements contain porous plate called sieve plate. • Sieve plate allows movement of ﬂ uid from one sieve element to the next.

Answer 16

• They are non-conducting cells. • Found alongside in each sieve tube element and connects with sieve tube element by numerous plasmodesmata • Nucleus and ribosomes of these cells also serve to adjacent sieve tube element • Some companion cells in leaves help in phloem loading and in other organs unloading

Answer 17

Growth involves irreversible increase of dry mass associated with the development of an organism. Often it is associated with increase of cell number as a result of producing more cells from the meristem accompanied by cell elongation. Plants continue growth throughout the life known as indeterminate growth.

Answer 18

Apart of the distribution pattern of xylem and phloem tissue structures of both monocot and dicot roots are more or less similar.

Answer 19

Epidermis protects inner parts while root hairs involve in the absorption of water and minerals.

Answer 20

Outermost cell layer is epidermis. Cells have unicellular outgrowths called root hairs.

Answer 21

Between epidermis and vascular cylinder there is a ground tissue known as cortex which is made up of mostly parenchyma cells with intercellular spaces.

Answer 22

Cortex mainly stores carbohydrates, and also transports water and minerals towards the endodermis.

Answer 23

Innermost single cell layer of the cortex is the endodermis. • Endodermis contains a suberin belt called casparian strip and no inter-cellular spaces.

Answer 24

Therefore, it blocks cortical apoplast from the vascular apoplast

Answer 25

Interior to endodermis there is a pericycle containing two or three parenchyma cell layers.

Answer 26

These cells in dicot roots have meristematic function and involve in the formation of lateral roots and secondary growth of the root.

Answer 27

Inner to pericycle there is vascular tissues as a solid core. Xylem can be found in the middle and it is star shaped in a cross section of a dicot root. Phloem is located in the groove between the arms of xylem.

Answer 28

In monocot roots, vascular tissue consists of a central core of parenchyma cells surrounded by a ring of alternating xylem and phloem

Answer 29

Pericycle in monocot roots is not meristematic

Answer 30

The outermost epidermal cell layer protects inner parts from desiccation and infections

Answer 31

The epidermis is interrupted by pores called stomata. Collenchyma cells may also be present just beneath the epidermis to provide strength.

Answer 32

• Ground tissue of monocot shoot is not differentiated into cortex and pith • The vascular bundles are scattered throughout the ground tissue in most monocot stems. • Each vascular bundle is surrounded by sclerenchyma. It consists of a xylem tissue and a phloem tissue but no cambium inbetween xylem and phloem.

Answer 33

• Vascular bundles arranged as a ring. Vascular bundle contains primary phloem towards cortex primary xylem towards pith and in-between a cambium tissue. • Outside vascular bundle, there is a cluster of sclerenchyma cell. • Inner to vascular bundles large pith which is also made up of parenchyma cells can be found.

Answer 34

Lateral shoots develop from axillary buds

Answer 35

Interior to epidermis is cortex mostly containing parenchyma cells

Answer 36

This occurs in stems and roots of woody perennial plants including, all gymnosperms species and many dicot species.

Answer 37

The vascular cambium adds secondary xylem (wood) towards primary xylem and secondary phloem towards primary phloem, increasing vascular ﬂ ow and support for the shoots

Answer 38

The cork cambium produces tough thick covering consisting mainly of wax impregnated cells that protect the stem from water loss and from invasion of insects, bacteria and fungi.

Answer 39

In a typical woody stem, the vascular cambium consists of a continuous cylinder of undifferentiated cells of often only a single cell layer in thickness, located outside the pith and primary xylem and to the inside of the cortex and primary phloem.

Answer 40

In a typical woody root, the vascular cambium forms laterally exterior to the primary xylem and interior to the primary phloem and pericycle.

Answer 41

• As these meristematic cells divides they increase circumference of the vascular cambium and also add secondary xylem to the inside of the cambium and secondary phloem to the outside. • Viewed in a cross section, the vascular cambium appears as a ring of initials.

Answer 42

• As these meristematic cells divides they increase circumference of the vascular cambium and also add secondary xylem to the inside of the cambium and secondary phloem to the outside. • Viewed in a cross section, the vascular cambium appears as a ring of initials.

Answer 43

Some initials are elongated and are oriented with their long axis parallel to the axis of stem or root. The other initials are shorter and oriented perpendicular to the axis of the stem or root.

Answer 44

They produce vascular rays-mostly parenchyma cells that connect secondary xylem and phloem, store carbohydrates and aid in wound repairing

Answer 45

• As the secondary growth continues over many years, layers of secondary xylem (wood) accumulate. • The walls of the secondary xylem cells are heavily ligniﬁed and account for the hardness and strength of wood. • During early stages of secondary growth, the epidermis pushed outwards, causing it to split, dry and falls off the stem or root • It is replaced by two tissues produced by cork cambium, a cylinder of dividing cells that arises in the outer layer of cortex in stems and in the outer layer of pericycle in the roots.

Answer 46

• Cork cambium produces cork cells to exterior. • Cork cambium and tissues it produces are collectively called periderm • As the cork cells mature, they deposit a waxy, hydrophobic material called suberin in their walls and they become dead cells.

Answer 47

• Some initials are elongated and are oriented with their long axis parallel to the axis of stem or root. • They produce cells such as tracheids, vessel elements, parenchyma and ﬁ bers of the xylem, as well as sieve-tube elements companion cells, phloem ﬁ bers and phloem parenchyma.

Answer 48

• The cork tissues function as a barrier that helps protect the stem or root from water loss, physical damages and pathogens.

Answer 49

• Each cork cambium and the tissues it produces comprise a layer of periderm which is impermeable to water and gasses.

Answer 50

• Further growth of stem or root breaks the layer of cork cambium and it lacks its meristematic activity and its cells become cork cells • A new cork cambium is initiated inside which with produce a new layer of periderm. • As new cells are added, the outer regions of cork will crack and peel off in many tree trunks. • Due to the tissue layers produced by vascular cambium and cork cambium, girth of the stem or root increases in secondary growth.

Answer 51

• Bark is all tissues out of the vascular cambium (cork is commonly and incorrectly referred to as bark). Its main components are secondary phloem and periderm.

Answer 52

HEART WOOD • As a woody plant ages, the older layers of secondary xylem no longer transport water and minerals. • These layers are called heartwood because they are close to the centre of the stem or root. • The heartwood is generally darker than sapwood because of resins and other compounds that permeate the cell cavities and help protect the core of the tree from fungi and wood-boring insects. SAP WOOD • The newest outer layers of secondary xylem, still transport xylem sap are known as sapwood. • Only the young secondary phloem functions in phloem translocation and old secondary phloem is sloughed off.

Answer 53

• Hard wood is the secondary xylem of dicot angiosperms while wood of gymnosperms are named soft wood • Xylem vessels are absent in soft wood

Answer 54

• In temperate regions, wood that develops early in spring is known as spring wood. This xylem tissue consists of xylem vessels with large lumens and thin walls. This structure maximizes delivery of water to new leaves. • The wood produced during rest of the growing season is called summer wood. These xylem tissues consist of xylem vessels with thick walls and small lumen, do not transport much water but provide more support.

Answer 55

• These two woods collectively known as an annual ring. A year’s growth appears as distinct ring in the cross section of most tree trunks and roots. Therefore age of the tree can be estimated by counting annual rings in trees growing in temperate regions.

Answer 56

• These two woods collectively known as an annual ring. * A year’s growth appears as distinct ring in the cross section of most tree trunks and roots. * Therefore age of the tree can be estimated by counting annual rings in trees growing in temperate regions.

Answer 57

• Length of the stem and branching pattern are designed to capture maximum light. • Plants grow tall to avoid shading from neighboring plants.

Answer 58

• Most tall plants have thick stem with strong mechanical support. • Woody plants undergo secondary growth thereby make their tall stem stronger. • Vines rely on other objects to reach higher levels to capture more light.

Answer 59

• There is a variety in branching pattern. • Some plants are unbranched and still others are well branched. • This variation in branching pattern enables the plant to absorb maximum light in the ecological niche it occupies.

Answer 60

• Size of the leaf vary, based on the place where the plant grows. • Largest leaves are found in plants growing in rain forests. • Smallest leaves are found in plant species inhabiting dry or very cold environments.

Answer 61

• This is the arrangement of leaves on the stem. • The arrangement may be one leaf, two leaves or several leaves per node. • Phyllotaxy helps the plant to capture maximum sunlight.

Answer 62

• Leaves may be horizontally oriented. • They capture light efﬁ ciently in low light conditions. • Some plants have vertically arranged leaves. e.g. Grasses • This is to avoid the possible damage caused by exposure of leaf to the over intense light. When leaves are nearly vertical, light rays are parallel to the leaf surfaces, so no leaves receive too much of light.

Answer 63

The exchange of gases occurs through stomata in the upper and lower epidermis. Epidermis is usually a single cell layer. In between the upper and lower epidermis, there is a ground tissue called the mesophyll. This tissue consists of parenchyma cells, specialized for photosynthesis.

Answer 64

In dicot leaves, stomata are, mainly found in the lower epidermis. The mesophyll consists of two distinct layers called palisade and spongy. Palisade mesophyll consists of elongated cells that are arranged in one or more layers. This can be found in the upper part of the leaf, just beneath the upper epidermis. The spongy mesophyll can be found between the palisade layer and lower epidermis. They are loosely arranged with many air spaces. Spongy mesophyll cells have less chloroplasts than in palisade mesophyll cells.

Answer 65

The vascular tissue of the leaf is continuous with vascular tissue of the stem. Veins in the leaf is highly branched (net like venation) in the mesophyll layer. Each vein is protected by a bundle sheath layer.

Answer 66

In monocot leaves, stomata are present in both lower and upper epidermis. Mesophyll is not differentiated into palisade and spongy layers. Chloroplasts are abundant in all mesophyll cells. Veins are parallelly arranged (parallel venation).

Answer 67

• ABA is produced in roots and leaves in response to water deﬁ ciency. • Production of ABA leads to close the stomata by removal of K+in guard cells. • This prevents the wilting of the plant.

Answer 68

• Stomata open during day and mostly closed at night. Light stimulates accumulation of K+ in guard cells. • Decrease in CO2 concentration in substomatal cavity lead to open stomata • Internal clock in the guard cells controlling their daily rhythm of opening and closing of stomata. • Environmental stresses such as drought, high temperature and wind can cause stomata to close during the day time.

Answer 69

• Active transport • Passive transport • Diffusion • Osmosis • Imbibition • Facilitated diffusion • Bulk ﬂ ow- long distance

Answer 70

• Active transport • Passive transport • Diffusion • Osmosis • Imbibitions • Facilitated diffusion • Bulk ﬂ ow- long distance

Answer 71

As land plants evolved and increased in number, competition for light, water and nutrients also increased. As a result, the size and complexity of plant body increased. Therefore the simple ways of transportation of water and material became inadequate leading to the evolution of vascular tissues, consisting of xylem and phloem to carryout long distance transport in plants.

Answer 72

e.g. the xylem transports water and minerals from roots to shoots. the phloem transports products of photosynthesis from where they are made or stored to where they are needed.

Answer 73

Passive transport occurs spontaneously, and it does not require metabolic energy (ATP). Movement of some materials across membranes takes place using ATP and that process is called an active transport.

Answer 74

Water and soluble materials can diffuse through the cellulose cell wall O2 and CO2 can diffuse through the plasma membrane

Answer 75

adsorption of water molecules by the cellulose cell walls.

Answer 76

adsorption of water molecules by the cellulose cell walls.

Answer 77

Free water is water molecules that are not bound to solutes or surfaces.

Answer 78

It is a long-distance transport method. This ﬂow does not occur through the membranes and occurs at much greater speed than diffusion. This method of transport is independent of solute concentration gradient.

Answer 79

*Water potential is related to potential energy of water molecules. *Any system that contains water has a water potential. Free water moves from regions of higher water potential to regions of lower water potential, if there is no barrier to its ﬂow. *Water potential is denoted by Ψ. Ψ is measured in a unit of megapascal (MPa). Arbitrary the Ψ of pure water in a container open to the atmosphere under standard conditions (at sea level and room temperature) is 0 MPa. *Both solute concentration and physical pressure can affect water potential; as expressed in the water potential equation. Ψ =Ψs + Ψp Ψ= water potential Ψs= solute potential Ψp= pressure potential

Answer 80

is directly proportional to the molarity of a solution

Answer 81

The solutes in plants are typically mineral ions and sugars.

Answer 82

When solutes are added, they bind water molecules and reduce free water molecules, reducing capacity of the water to move and do work. In this way an increase in solutes has a negative effect on water potential. Therefore, Ψs of a solution is always expressed as a negative number. As the solute concentration increases, Ψs will become more negative. e.g: Ψs of the 0.1M sugar solution is -0.23MPa

Answer 83

Ψp can be positive or negative relative to atmospheric pressure.

Answer 84

e.g: Ψp of a xylem vessel is usually less than -2 MPa as xylem vessels are under tension (negative pressure) Ψp of a living cell is a positive value because living cell is usually under positive pressure due to osmotic uptake of water.

Answer 85

Ψp= 0 ;Ψs= Ψ

Answer 86

since the external solution has a lower (more negative) water potential, water diffuse out of the cell. The protoplast of the cell shrinks and pulls away from the cell wall. This process is known as plasmolysis.

Answer 87

The cell has a lower water potential than the pure water as it contains solutes. Therefore, water enters the cell by osmosis. Then the protoplast of the cell begins to swell and press the plasma membrane against the cell wall. The partially elastic cell, exerting a turgor pressure, contains the pressurized protoplast. Therefore, Ψp is increased gradually.

Answer 88

The maximum value of Ψp= Ψs of the cell. Therefore, Ψ becomes 0. This matches the water potential of extracellular environment, 0 Mpa. Then a dynamic equilibrium is formed and there is no further net water movement. If the cell has the maximum value for Ψp, (it equal to the Ψs of the cell) the cell is said to be in fully turgid state. (fully turgid or fully ﬂaccid cells are not found in nature).

Answer 89

it is stiffened and is very rigid. Therefore, turgor pressure helps support of non woody plants

Answer 90

Turgor pressure is also important in cell elongation. Loss of turgor results in wilting, a condition where leaves and stem droop.

Answer 91

his absorption takes place across the plasma membrane. Water can enter root hair by osmosis, a passive movement along the concentration gradient. But in the root hairs concentration of mineral ions is greater than that of soil solution. K+ concentration in the root hair is hundreds of time greater than in the soil solution. Therefore, mineral ions transport occurs against concentration gradient, by an active transport.

Answer 92

The soil solution is also absorbed into hydrophilic walls of the epidermal cells and passes freely along the cell walls and the extracellular spaces into the root cortex.

Answer 93

The endodermis, the innermost layer of cells in the cortex, functions as the last check point for selective passage of the minerals from the cortex into the vascular cylinder. All materials which enters root through cell walls and extracellular spaces should cross the membranes of endodermis. Therefore, unwanted materials can be selectively excluded. Thus water and minerals cannot cross the endodermis and enter the vascular cylinder via apoplast. DUE TO THE CASPARIAN STRIPS: Therefore, water and minerals cross the selectively permeable plasma membrane before entering the vascular tissue and keep unneeded and toxic materials out. The endodermis also prevents solutes that have accumulated in the xylem from leaking back into the soil solution.

Answer 94

Endodermis blocks apoplastic route by a barrier located in the transverse and radial walls of endodermal cells, called the casparian strips. It is a belt made of suberin which is impervious to water and mineral salts. Thus water and minerals cannot cross the endodermis and enter the vascular cylinder via apoplast.

Answer 95

includes cell walls, extracellular spaces and the interior of dead cells such as vessel elements and tracheids.

Answer 96

entire mass of cytosol of all living cells in a plant, as well as plasmodesmata, the cytoplasmic channels that interconnect them

Answer 97

In the symplastic route, water and solutes move along the continuum of cytosol. This route requires substance to cross a plasma membrane once, when they ﬁ rst enter the plant. After entering one cell, substances can move from cell to cell via plasmodesmata.

Answer 98

sucrose (as 30% by weight) and it may also contain amino acids, hormones and minerals.

Answer 99

Plant leaves

Answer 100

roots, stems, buds and fruits are sinks

Answer 101

tubers and bulbs

Answer 102

pressure ﬂow hypothesis.

Answer 103

1. Loading of sugar into the sieve tube reduces water potential inside the sieve tube elements at the source 2. This causes the sieve tube to take up water from the xylem by osmosis. 3. This uptake of water generates a positive pressure that forces the sap to ﬂ ow along the tube 4. The pressure is reduced by unloading of sugar and consequent loss of water from phloem to the xylem at the sink

Answer 104

through stomata.-stomatal transpiration upto some extent through cuticle-cuticular transpiration and through lenticels- lenticular transpiration. About 95% of water in plants is lost through stomatal transpiration.

Answer 105

In the day time, air in the intercellular air spaces is saturated with water vapour because they are in contact with the moist cell walls. Normally air outside the plant is drier than inside. Hence water potential of outside air is lower than that of inside. Therefore water vapour in the air spaces of the plant diffuses down its water potential gradient and exits the plant.

Answer 106

1. Light intensity 2. Temperature 3. Humidity 4. Wind speed 5. Concentration of CO 6. Available water in soil

Answer 107

* Stomata usually open in the light and close in darkness. * With the increase of light intensity the rate of transpiration increases.

Answer 108

*In the presence of light, the external factor which has the greatest effect on transpiration is temperature. *The higher the temperature, the greater the rate of evaporation of water from mesophyll cells which result the greater saturation of the leaf atmosphere with water vapour. *At the same time, a rise in temperature lowers the relative humidity of the air outside the leaf. *Both events result in a steeper concentration gradient of water molecules from leaf to external atmosphere. *The steeper this gradient is the faster the rate of diffusion.

Answer 109

*In the presence of light, the external factor which has the greatest effect on transpiration is temperature. *The higher the temperature, the greater the rate of evaporation of water from mesophyll cells which result the greater saturation of the leaf atmosphere with water vapour. *At the same time, a rise in temperature lowers the relative humidity of the air outside the leaf. *Both events result in a steeper concentration gradient of water molecules from leaf to external atmosphere. *The steeper this gradient is the faster the rate of diffusion.

Answer 110

*Low humidity outside environment of the leaf increases transpiration, because it makes the diffusion gradient of water vapour from the moist leaf atmosphere to drier external atmosphere. *As the concentration of water vapour in the external atmosphere is high when humidity rises, the diffusion gradient becomes less steep result in lower transpiration.

Answer 111

*Low humidity outside environment of the leaf increases transpiration, because it makes the diffusion gradient of water vapour from the moist leaf atmosphere to drier external atmosphere. *As the concentration of water vapour in the external atmosphere is high when humidity rises, the diffusion gradient becomes less steep result in lower transpiration.

Answer 112

*In still air, a shell of highly saturated air builds up around the leaf thus reducing the steepness of the diffusion gradient between leaf atmosphere and external atmosphere which makes the transpiration rate low. *In windy condition, ﬂow of air will generally sweep away the shell. Therefore, windy condition increases transpiration rate.

Answer 113

As soil dries out, water usually binds more tightly to soil particles reducing the amount of available water. The soil solution becomes more concentrated and its water potential decreases. Therefore, tendency for water to enter by osmosis is lower. This reduces water uptake by plants and as a result transpiration rate is also reduced. There is greater resistance to movement of water through the plant due to less steep water potential gradient from the soil through the plant to the atmosphere.

Answer 114

Some substances can use more than one route. The least resistence for the transport is found in apoplastic route. Therefore, more water use apoplastic route.

Answer 115

1. Distribute minerals and water throughout the plant. 2. Ascent of water in the xylem. 3. Uptake of water and minerals by roots from the soil solution.

Answer 116

Guttation ﬂuid differs from dew, which is condensed moisture of the atmosphere.

Answer 117

Even in plants that display guttation, root pressure cannot match the water loss by transpiration after sun rise and therefore no guttation is seen in the day time, because then xylem sap is not pushed but pulled upward by transpiration.

Answer 118

hydathode which are formed by special groups of cells located near the ends of small veins and does not take place through the stomata.

Answer 119

e.g. Alocasia, Colocasia

Answer 120

Plants are photoautotrophs which utilizes light energy in order to synthesize organic molecules from inorganic material

Answer 121

mutualism, parasitism, and commensalism.

Answer 122

legume root nodules with nitrogen ﬁxing bacteria (Rhizobium) mycorrhizae- symbiotic association of roots of higher plants with fungi corolloid root of Cycas with Anabaena

Answer 123

epiphytic orchids

Answer 124

Loranthus and host plant

Answer 125

Cuscuta (dodder plants)

Answer 126

They live in habitats where the soil is poor in nitrogen and other minerals.

Answer 127

Nepenthes, Drosera , Utricularia

Answer 128

C,O,H,N,P,S,K,Ca, Mg (9 elements)

Answer 129

Cl, Fe, Mn, B, Zn, Cu, Ni, Mo

Answer 130

The life cycles of all land plants exhibit alternation of generations which means the presence of haploid generation and diploid generation alternatively, with each producing the other.

Answer 131

The two multicellular body forms that alternate in the life cycles of land plants are the haploid gametophyte and diploid sporophyte which are morphologically different.