How cells work together II

Question 1

Root system

Answer 1

A root system is comprised of the roots.

Question 2

Shoot system

Answer 2

The shoot system is comprised of the stems and leaves.

Question 3

Root

Answer 3

It is the organ that anchors a vascular plant in the soil, absorbs minerals and water, and often stores carbohydrates.

Question 4

Taproot

Answer 4

Tall erect plants with large shoot masses generally have a taproot system, consisting one main vertical root called the taproot.

Question 5

Lateral roots

Answer 5

In taproot systems, the role of absorption is restricted largely to tips of lateral roots. The lateral roots are the ones that branch of from the tap root. The lateral roots destructively push through the cortex and epidermis until they emerge from the established root.

Question 6

Monocots

Answer 6

A class of angiosperm that typically has one cotyledon (seed leaf), and is named accordingly.

Question 7

Eudicots

Answer 7

A class of angiosperm that typically has two cotyledons (seed leaves), and it is named accordingly.

Question 8

Root hairs

Answer 8

In most plants, the absorption of water and minerals occurs primarily near the tips of elongating roots, where a vast numbers of root hairs, thin, fingerlike extensions of root epidermal cells, emerge and increase the surface area enormously.

Question 9

Stem

Answer 9

It is a plant organ bearing leaves and buds. It’s main function is to elongate and orient the shoot in a way that maximizes photosynthesis by the leaves. It also elevates reproductive structures, which facilitates dispersal of pollen and fruit.

Question 10

Nodes

Answer 10

Each stem consists of an alternating system of nodes, which is the point where leaves are attached to the stem.

Question 11

Internodes

Answer 11

They are the stem segments between the nodes.

Question 12

Apical bud

Answer 12

The growing shoot tip is the apical bud, and that is where most of the growth is concentrated.

Question 13

Axillary bud

Answer 13

The buds that are turned in an upward angle, but can potentially turn into a lateral branch or a thorn or flower.

Question 14

Leaf

Answer 14

In vascular plants the leaf is the main organ responsible for photosynthesis. They also exchange gases with the atmosphere, dissipate heat and defend themselves from herbivores and pathogens.

Question 15

Blade

Answer 15

A leaf consists of a flattened blade, and a stalk, the petiole.

Question 16

Petiole

Answer 16

A leaf consists of a flattened blade, and a stalk, the petiole.

Question 17

Veins

Answer 17

Monocots and eudicots differ in the arrangement of veins, the vascular tissue of plants. Most monocots have parallel major veins of equal diameter that run the length of the blade. Eudicots generally have a branched network of veins arising from a major vein, the midrib, that runs down the center of the blade.

Question 18

Rhizomes

Answer 18

A horizontal shoot that grows just below the surface. Vertical shoots emerge from axillary buds on the rhizome.

Question 19

Stolons

Answer 19

Stolons are horizontal shoots that grow along the surface. These runners enable a plant to reproduce asexually, as plantlets form at nodes along each runner.

Question 20

Tubers

Answer 20

Enlarged ends of rhizomes or stolons specialized for storing food, like potatoes, the eyes of potatoes are axillary buds that mark the nodes.

Question 21

Dermal tissue system

Answer 21

It is the plants outer protective covering. Like our skin it protects against physical damage and pathogens.

Question 22

Epidermis

Answer 22

In nonwoody plants, the dermal tissue system is called the epidermis, which is a layer of tightly packed cells. The epidermis also has specialized characteristics in each organ, like root hair is an extension of an epidermal cell near the tip of the root.

Question 23

Cuticle

Answer 23

In leaves and stems, the cuticle, a waxy coating on the epidermal surface, helps prevent water loss.

Question 24

Periderm

Answer 24

In woody plants, the epidermis is replaced with a protective tissue called periderm in older regions of stem and roots.

Question 25

Vascular tissue system

Answer 25

The system is there to facilitate transport of materials through the plant and to provide mechanical support. The two types of vascular tissues are called xylem and phloem.

Question 26

Xylem

Answer 26

It conducts water and dissolved minerals upward from the roots to the shoots.

Question 27

Phloem

Answer 27

It transports sugars, the products of photosynthesis, from where they are made, (usually in the leaves) to where they are needed or stored, usually roots or sites of growth, such as developing leaves and fruit.

Question 28

Stele

Answer 28

The vascular tissue of root and stem is collectively called stele. And the arrangement of stele varies, depending on the species and organ.

Question 29

Ground tissue system

Answer 29

Tissues that are neither dermal or vascular, are part of the ground tissue system. This is not just a filler, it may include cells specialized for functions such as storage, photosynthesis, support, or short distance transport.

Question 30

Pith

Answer 30

Ground tissue that is internal to the vascular tissue is known as pith.

Question 31

Cortex

Answer 31

Ground tissue that is external to the vascular tissue is known as cortex.

Question 32

Tendrils

Answer 32

Tendrils are used for one plant to cling to another. It lassoes support for itself. Tendrils are typically modified leaves, however they can be modified stems like in grapevines.

Question 33

Spines

Answer 33

The spines of cacti are actually leaves, photosynthesis is carried out by the fleshy green stems.

Question 34

Storage leaves

Answer 34

Bulbs such as a cut onion, have a short underground stem and modified leaves that store food. The storage leaves are the layers, the stem is the tiny root at one end.

Question 35

Reproductive leaves

Answer 35

The leaves of some succulents, produce adventitious plantlets which fall off the leaf and take root in the soil.

Question 36

Parenchyma cells

Answer 36

Mature parenchyma cells have primary walls that are relatively thin and flexible, and most lack secondary walls. When mature, they have a large central vacuole. They perform most of the metabolic functions of the plant by synthesizing and storing organic products. For instance, photosynthesis happens in within chloroplasts of the parenchyma cells in the leaf. Some store starch, and the fleshy tissue of many plants are composed of these cells also. Most of them retain the ability to divide and differentiate into other kinds of plant cells, under particular conditions, like while repairing a wound. It is also possible to grow an entire plant from one of these cells.

Question 37

Collenchyma cells

Answer 37

Grouped in strands, these cells comprise the stem. They help support the young parts of the plant shoot. They are generally elongated cells that have a thicker primary wall than parenchyma cells though not evenly. Young stems and petioles often have strands of collenchyma cells just under the layer of epidermis. They provide flexible support without hindering growth, and at maturity, the cells are living and flexible, elongating with the stems and leaves they support.

Question 38

Sclerenchyma cells

Answer 38

These cells are also supporting elements in the plant, but are less flexible than the collenchyma cells. In sclerenchyma cells, the second cell wall, that is produced after cell elongation has ceased, is thick and contains large amounts of lignin. Mature cells cannot elongate, and they occur in regions of plants that have stopped growing in length. They are so specialized at support that that many are dead at functional maturity, but they produce the second cell wall before the protoplasts (the living parts of the cell) dies. The rigid walls have then become the plants skeleton, which can support the plant up to 100’ds of years.

Question 39

Lignin

Answer 39

It is a relatively indigestible strengthening polymer that accounts for more than a quarter of the dry mass of wood. Lignin is present in all vascular plants but not in bryophytes.

Question 40

Sclereids

Answer 40

There are two types of sclerenchyma cells, which are specialized for strengthening and support. One is called sclereid, the other fibers. The sclereid is boxier and irregular in shape, and they have very thick lignified secondary walls. It is what supplies the hardness to nutshells and seed coats and the gritty texture to pear fruits.

Question 41

Fibers

Answer 41

There are two types of sclerenchyma cells, which are specialized for strengthening and support. One is called sclereid, the other fibers. Fibers are usually grouped in strands, and are long, slender and tapered. Some are commercially used, such as hemp fibers for making rope and flax fibers for weaving into linen.

Question 42

Water-conducting cells of the Xylem

Answer 42

There are two types of water-conducting cells, tracheid’s and vessel elements. They are tubular, elongated cells that are dead and lignified at functional maturity.

Question 43

Tracheids

Answer 43

They are long, thin cells, with tapered ends. Water moves from cell to cell mainly through pits, where it does not have to cross thick secondary walls.

Question 44

Vessel elements

Answer 44

They are generally wider, shorter, thinner walled and less tapered than tracheids. They are aligned end to end, forming long pipes known as vessels that in some cases, are visible to the naked eye. The end walls of the vessels have perforation plates that enable water to flow freely through the vessels.

Question 45

Tracheids and vessel elements

Answer 45

They occur in the xylem of all vascular plants, and in addition to tracheids, most angiosperms as well as a few gymnosperms and a few seedless vascular plants have vessel elements. When the living cellular content of a tracheid or vessel element disintegrate, the cells thickened walls can flow, and the secondary wall is often interrupted by pits, thinner regions where only primary walls are present, so that water can migrate laterally between neighboring cells. The secondary wall in tracheids and vessel elements are hardened with lignin. This provides support and prevents collapse under the tension of water transport.

Question 46

Sugar-conducting cells of the Phloem

Answer 46

These cells are alive when functioning at maturity, and in seedless plants and gymnosperms, sugars and other organic nutrients are transported through long narrow cells called sieve cells. In the phloem of angiosperms, these nutrients are transported through sieve tubes, which consist of chains of cells called sieve-tube elements.

Question 47

Sieve-tube

Answer 47

Sieve tube elements or sieve tube members are alive, but they lack a nucleus, ribosomes, a distinct vacuole, and cytoskeletal elements. The missing elements enable nutrients to pass more easily through the cell.

Question 48

Sieve plates

Answer 48

The end walls between sieve tube elements are called sieve plates, and they have pores to facilitate the flow of fluid from cell to cell along the sieve tube.

Question 49

Companion cell

Answer 49

Along each sieve tube element is a nonconducting cell, called a companion cell, which is connected to the sieve tube element by numerous plasmodesmata. The nucleus and ribosomes of the companion cell, serve not only the cell itself, but also the adjacent sieve tube element. In some plants, the companion cell in leaves also help load sugars into the sieve tube elements, which then transports it to other places in the plant.

Question 50

Intermediate growth

Answer 50

Plant growth is not limited to an embryonic or juvenile period, but grows continuously throughout the plants life, this is known as intermediate growth. At any time, a typical plant has embryonic, developing and mature organs, except for in dormant periods.

Question 51

Meristems

Answer 51

Plants can keep growing, because they have perpetually dividing unspecialized tissue called meristems that divide when the conditions permit, leading to new cells that elongate and become specialized.

Question 52

Determinate growth

Answer 52

Most animals, and some plant organs undergo something called determinate growth, that is they stop growing after reaching a certain size.

Question 53

Apical meristems

Answer 53

There are two main types of meristems. Apical meristems located at the tips of the roots and shoots and in axillary buds of shoots, provide additional cells that enable growth in length, a process known as primary growth. The shoot apical meristem is a dome-shaped mass dividing cells at the shoot of the tip.

Question 54

Primary growth

Answer 54

Primary growth allows roots to extend throughout the soil, and the shoots to increase their exposure to light. In herbaceous (nonwoody) plants, primary growth produces all, or almost all of the plant body.

Question 55

Secondary growth

Answer 55

In woody plants, they also grow in circumference, in parts that are no longer growing in length, this is called secondary growth.

Question 56

Lateral meristems

Answer 56

There are two main types of meristems. Lateral meristems causes the secondary growth, and is called the vascular cambium and cork cambium. These cylinders of dividing cells extend along the length of roots and stems.

Question 57

Vascular cambium

Answer 57

This adds layers of vascular tissue called secondary xylem (wood) and secondary phloem.

Question 58

Cork cambium

Answer 58

This replaces the epidermis with thicker, tougher periderm.

Question 59

Root cap

Answer 59

The tip of the root is covered with a thimble like root cap, which protects the delicate apical meristem as the root pushes through the abrasive soil during primary growth. The cells of the root cap also secrete a polysaccharide slime that lubricates the soil around the tip of the root. Growth occurs just behind the tip in 3 overlapping zones of cells at successive stages of primary growth.

Question 60

Zone of cell division

Answer 60

It includes the root apical meristem and its derivations. New roots are produced in this region.

Question 61

Zone of elongation

Answer 61

A few millimeters behind the tip of the root is the elongation zone, where most of the growth occurs as root cells elongate. This pushes the tip farther into the soil. Meanwhile the root apical meristem keeps adding cells to the younger end of the elongation zone. Many cells begin specializing before they have finished elongating.

Question 62

Zone of differentiation

Answer 62

In this part, the cells finish differentiation, which started in the zone of elongation, and they mature, becoming distinct cell types.

Question 63

Endodermis

Answer 63

The innermost layer of the cortex is called the endodermis, a cylinder one cell thick that forms the boundary with the vascular cylinder. It is a selective barrier that regulates passage of substances from the soil into the vascular cylinder.

Question 64

Pericycle

Answer 64

Lateral roots arise from meristematically active regions of the pericycle, the outermost cell layer in the vascular cylinder, which is adjacent to and just inside the endodermis.

Question 65

Leaf primordia

Answer 65

Leaves develop from leaf primordia, projections shaped like a cows horns that emerge along the sides of the shoot apical meristem. Within a bud, young leaves are spaced close together, because the internodes are very short. Shoot elongation is due to the lengthening of internode cells below the shoot tip.

Question 66

Apical dominance

Answer 66

Because of chemical communication by plant hormones, the closer an axillary bud is to an active apical bud, the more inhibited it is, a phenomenon called apical dominance. If an animal eats the end of the shoot or if shading results in the light being more intense on the side, then the apical dominance is disrupted.

Question 67

Stomata

Answer 67

The epidermis of leaves is interrupted by pores called stomata, (singular stoma) which allow exchange of CO2 and O2 between the surrounding air and the photosynthetic cells inside the leaf. In addition to regulating CO2 uptake, the stomata are major avenues for the evaporative loss of water. The term stoma can refer to the stomatical pore, or the entire stomatical complex consisting of a pore flanked by 2 specialized epidermal cells called guard cells.

Question 68

Guard cells

Answer 68

The guard cells regulate the opening and closing of the pore.

Question 69

Mesophyll

Answer 69

The leaf’s ground tissue, called the mesophyll, is sandwiched between the upper and lower epidermal layers. It consists mainly of parenchyma cells specialized in photosynthesis. The mesophyll in many eudicot leaves has two distinct layers, palisade and spongy.

Question 70

Palisade mesophyll

Answer 70

The palisade mesophyll consists of one or more elongated layers of parenchyma cells on the upper part of the leaf.

Question 71

Spongy mesophyll

Answer 71

The spongy mesophyll is below the palisade mesophyll and they are more loosely arranged, with a labyrinth of air spaces through which CO2 and O2 circulate around the cells and up to the palisade region. The airspace is particularly large in the vicinity of stomata, where CO2 is taken up from the outside air and O2 is released.

Question 72

Bark

Answer 72

Cork is more commonly referred to as bark. In biology, bark includes all tissues external to the vascular cambium (wood). Its main components are the secondary phloem (produced in the vascular cambium) and, external to that, the most recent periderm and all the older layers of periderm.

Question 73

Lenticels

Answer 73

Dotting the periderm are small, raised areas called lenticels, in which there is more space between cork cells, enabling living cells within a woody stem or root to exchange gases with the outside air. They often appear as horizontal slits.

Question 74

Herbivory

Answer 74

Animals eating plants, is a stress that plants face in any ecosystem. The mechanical damage caused by herbivores reduces the size of plants, hindering their ability to acquire resources, and can restrict growth, because they need to redirect energy towards reparation. It also opens them up to infections. Therefore plants have evolved many kinds of defenses against animals, like thorns.

Question 75

Pathogen-associated molecular patterns (PAMPs)

Answer 75

The first line of immune defense called PAMP-triggered immunity, depends on the plant’s ability to recognize PAMPs molecular sequences that are specific to certain pathogens. Plants do not have an adaptive immune system, they neither generate T cell responses nor possess mobile cells that detect or attack pathogens. PAMP recognition in plants trigger a chain of signaling events that lead to the local production of broad-spectrum anti-microbial chemicals called phytoalexins, which are compounds having fungicidal and bactericidal properties. The plant cell wall is also further toughened.

Question 76

Effectors

Answer 76

PAMP triggered immunity can be overcome by the evolution of pathogens that evade detection by the plant. These pathogens deliver effectors, which are pathogen-encoded proteins that cripple the plant’s innate immune system, directly into plant cells. For example, some bacteria deliver effectors that block the perception of flagellin. These effectors allow the pathogen to redirect the host’s metabolism to the pathogen’s advantage. The effector-triggered immunity also stimulates the formation of lignin and the cross-linking of molecules within the within the plant cell wall, responses that hinder the spread of the pathogen to other parts of the plant.

Question 77

Hypersensitive response

Answer 77

The hypersensitive response refers to the local tissue death that occurs at and near the infection site. In many cases, the hypersensitive response restricts the spread of a pathogen. The hypersensitive response is initiated as part of the effector-triggered immunity. The hypersensitive response is part of a complex defense response that involves the production of enzymes and chemicals that impair the pathogen’s cell wall integrity, metabolism, or reproduction. The hypersensitive response results in localized lesions on a leaf. As “sick” as such a leaf appears, it will still survive, and its defensive response will help protect the rest of the leaf.

Question 78

Systemic acquired resistance

Answer 78

While the hypersensitive response is localized and specific, the pathogen invasions can also produce signaling molecules that “sound the alarm” of infection in the whole plant. The systematic acquired resistance is then the result of the plant-wide expression of defense genes. It is nonspecific, providing protection against a diversity of pathogens that can last for days.

Question 79

Salicylic acid

Answer 79

A signaling molecule called methylsalicylic acid is produced around the infection site, carried by the phloem throughout the plant, and then converted to salicylic acid in areas remote from the sites of infection. Salicylic acid activates a signal transduction pathway that readies the defense system to respond rapidly to another infection.