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Grade 10 Biology > Anatomy of dicotyledonous plants- Roots and stems > Flashcards

Anatomy of dicotyledonous plants- Roots and stems Flashcards

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1
Q

What is the cotyledon in angiosperms

A

The cotyledon is part of the seed of the plant

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2
Q

What classifies the flowering plants (angiosperms)

A

The number of cotyledons (mono or di)

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3
Q

Name and describe the types of roots

A
  1. Tap root
    - primary root
    - embryonic radicle that grows and develops further
  2. Adventist root
    - any root that develops from any other plant organ other than a root
  3. Lateral root
    - secondary root
    - develop from another root (branch of the root)
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4
Q

Name and describe the two major types of root systems

A
  1. Taproot system
    - root system compromising one primary root and many secondary roots branching off the primary root
    - eg. carrot/beetroot where the roots serve a storage function
    - they are found in dicotyledonous plants
  2. Fibrous root system
    - system with no dominant primary root but many secondary roots of similar sizes
    - fibrous(adventitious) root systems are common in monocotyledons
    - eg. coconut/grass
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5
Q

What are the functions of roots

A
  1. Anchor the plant in the soil
  2. Absorb water an minerals from the soil and transport it to the rest of the body
  3. Store reserve organic nutrients. Although all roots contain a reserve, some roots are especially adapted for this function
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6
Q

Describe the apical meristem on the exterior region of roots

A
  1. Meristematic region (constantly forming new cells)

2. Allows growth of root tips

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7
Q

Describe the root cap

A

A slimy layer of cells that covers and protects the apical meristem

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8
Q

Describe the area of elongation on the exterior region of roots

A
  1. Directly above the meristematic region
  2. New cells are starting to grow in this region
  3. Cells can begin to differentiate to form Xylem and Phloem
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9
Q

Describe the root hair region on the exterior region of roots

A
  1. Part of the root where most water absorption takes place

2. Is characterised by unicellular, epidermal outgrowths (root hairs) with increase the absorption surface of the root.

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10
Q

Describe the permanent region on the exterior region of roots

A
  1. The lateral roots originate and start to branch out
  2. Increases the absorption surface. Water absorption can also take place in the region where the root has not yet been surrounded by a waterproof layer of cork
  3. Anchor the plant more firmly in the soil
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11
Q

Describe the epidermis in roots

A
  1. Also known as rhizodermis
  2. Single layer of living cells without chloroplasts
  3. No cuticle or stomata
  4. Most develop into root hairs, unicellular outgrowths, adapted to absorb water ad dissolved minerals from the soil solution
  5. The function is the absorption of water and dissolved nutrients
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12
Q

Describe the exodermis of roots

A
  1. The outer layer that takes over the functions of the epidermis in older roots
  2. Consists of cork type cells and permeable cells
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13
Q

Describe the cortex of roots

A
  1. Consists of a number of layers of living parenchyma cells with intercellular air spaces
  2. The cells are usually colourless but in aerial roots of epiphytes (plants that grow completely above ground) they contain chloroplasts
  3. The endodermis is a layer of cells that separates the cortex from the central cylinder, and will control the passage of water to the central cylinder
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14
Q

Describe the endodermis of roots

A
  1. Layered brick shaped cells
  2. The radial and transverse walls (within the cortex layers) of the endodermis have thickened cork strips (casparian bands)
  3. The radial and transverse walls are covered with a waterproof substance (suberin)
  4. The casparian bands direct the movement of water from the cortex to the central cylinder
  5. In monocotyledons, the thickened endodermis assumes the function of the cortex and the epidermis
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15
Q

Describe the casparian bands of roots

A
  1. The radial and transverse walls of the endodermis cells are filled with strips of waterproof lignin and suberin forming the bands of caspary
  2. The thickenings occur in the region of elongation (the region a little above the tip of the root, up to the more mature root hair region)
  3. The casparian bands prevent water from moving through the cell walls into the cytoplasm of the endodermis cells to control the absorption of water
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16
Q

Describe the pericycle of roots

A
  1. Found inside the endodermis and consists of thin walled cells without intercellular air spaces; usually one cell layer, rarely up to 3 cell layers wide
  2. Possesses latent meristematic properties and can give rise to lateral roots/ vascular cambium that arises in older roots which thickens secondary
  3. In dicots, the cork cambium differentiates from the pericycle
  4. The cells can be sclerenchymatic where the roots do not have secondary thickenings (in older monocotyledonous roots)
  5. On the inside of the pericycle are the vascular tissue (Xylem and Phloem)
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17
Q

Describe the vascular tissue on roots

A
  1. In the middle, the xylem is arranged in the form of a cross or a five pointed star
  2. In the inlets there are groups of phloem
  3. Vascular cambium develops between teh xylem and phloem to give rise to secondary xylem and phloem, thus causing the increasing thickness of the root
  4. The xylem thickens forming the central cylinder that transports water and dissolved mineral salts upward into the plant, and the phloem is squeezed against the endodermis
  5. The phloem and cortex later becomes part of the bark of an older root
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18
Q

What kind of stems can we find

A

herbaceous and woody stems

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19
Q

What are the functions of stems

A
  1. Support for the plant as it holds the leaves, flowers and fruits upright above the ground.
  2. They keep the leaves in light for photosynthesis and provide attachment for flowers and fruits so pollination can take place
  3. Transport of water, mineral salts and sugars between roots and shoots in the xylem and phloem
  4. Storage of nutrients
  5. Production of new living tissue: stems contain meristematic tissue which generates new living tissue
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20
Q

What is responsible for primary growth in stems

A

Stems grow longer from the apical growing tips of the stems

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21
Q

What is responsible for secondary growth in stems

A

The stalk growths in thickness and no longer forms tissue for strength and support but rather for transport and metabolic activities

Secondary thickening occurs in the cambium

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22
Q

What are the apical/terminal buds

A

tips of the stems

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23
Q

What do the apical/terminal buds consist of

A

Meristematic tissue, which is responsible for longitudinal growth and they are covered with bud scales for protection

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24
Q

What is formed in the terminal buds of the stem

A

Auxins (hormones) which stimulate cell division and elongation, phototropism and various other processes

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25
Q

What do the lateral/axillary buds do

A

They develop into new stems/leaves/flowers

26
Q

What are lenticels

A

small, wart like spots found everywhere on younger stems in older plants

27
Q

What do lenticels do

A
  1. Responsible for gas exchange
  2. Stomata are found on young green stalks, but when the stalk grows slightly older and bark begins to form, gas exchange is taken over by the lenticels
28
Q

What are the main regions of dicotyledonous stems

A
  1. Epidermis
  2. Cortex
  3. Central cylinder
29
Q

Describe the epidermis in stems

A

It is a single layer of cells covering the stem and it is covered by a waxy cuticle. It may posses hairy outgrowths known as trigomes, as well as stomata with guard cells

30
Q

What does the cuticle on the epidermis of stems do

A

Helps prevent water loss and drying out of inner tissues

31
Q

What is the function of the epidermis

A

To protect underlying tissues therefor the epidermal cells are tightly packed and have thickened walls

32
Q

What are the stomata on the epidermis responsible for

A

Transpiration and gas exchange, for respiration and photosynthesis

33
Q

What is the cortex

A

A region consisting of the collenchyma, parenchyma and endodermis

34
Q

Describe the collenchyma of the cortex

A
  1. It is a few layers of living cells that lie beneath the epidermis
  2. The cells don’t posses lignin even though they are unevenly thickened (thickened corners but have thin walls in other places)
  3. The thickened corners strengthen the stem and provide support, while the thin walled parts provide flexibility in the wind
  4. Contain chloroplasts (photosynthesis)
35
Q

Describe the parenchyma of the cortex

A
  1. Found beneath the collenchyma cells and occupies most of the cortex
  2. The cell walls are thin and there are intercellular spaces for gas exchange
  3. Stores manufactured organic foods (mainly starch) produced elsewhere in the plant
36
Q

Describe the endodermis of the cortex

A
  1. Single layer of brick like cells that form the inner layer of the cortex
  2. Not as clearly visible as it is in the root, can be absent in some stems
  3. Starch can also be sometimes stored in the endodermis and is known as a starch sheath
37
Q

What does the central cylinder consist of

A

The pericycle, vascular bundles and marrow

38
Q

Describe the pericycle

A
  1. Commonly found at roots and in lower plants also the stem
  2. In the higher vascular plants a clear layer of cells is often not present
  3. The pericycle, if present, may contain thin walled parenchyma cells or sclerenchyma cells with relatively thin or very thick cell walls
  4. In plants undergoing secondary growth, the pericycle contributes to the formation of the vascular cambium and also the cork cambium
39
Q

Describe the central cylinder/ vascular bundles

A
  1. Typically arranged in a circle within the pericycle of the dicotyledonous plant
  2. Its protected by sclerenchyma on the outside which occurs in strands called the sclerenchyma cap/pericycle cap
  3. Adult vascular bundles consist of water conducting xylem, cambium and food conducting phloem
  4. A layer of cambium between the xylem and phloem is called the vascular cambium/fascicular cambium
  5. The phloem is located outside of the bundle and the xylem in the middle. They are separated by meristematic tissue (cambium) which is responsible for secondary thickening
40
Q

Describe the pith/medulla

A
  1. Occupies the large, central part of the stem
  2. Made up of thin walled parenchyma cells containing intercellular spaces
  3. Where the parenchyma extends between vascular bundles as thin bands it is known as medulla rays and can be continuous with the pith and cortex of the parenchyma
  4. The cells of the pith store water and starch, while the intercellular spaces allow for gas exchange
  5. The medulla rays facilitate transport from xylem and phloem to the inner and outer parts of the stem
41
Q

What is the function of epidermis in dicotyledonous stems

A

protects the underlying tissue

42
Q

What is the function of cuticle in dicotyledonous stems

A

prevents water loss

43
Q

What is the function of stomata in dicotyledonous stems

A

allows gas exchange

44
Q

What is the function of collenchyma in dicotyledonous stems

A

strengthens the stem and acts as supporting tissue that keeps the stem upright. can contain chloroplasts for photosynthesis

45
Q

What is the function of parenchyma in dicotyledonous stems

A

stores organic substances and the intercellular air spaces allow for gas exchange

46
Q

What is the function of endodermis in dicotyledonous stems

A

stores starch

47
Q

What is the function of sclerenchyma fibres in dicotyledonous stems

A

protect the vascular bundles and strengthen and support the stem

48
Q

What is the function of xylem in dicotyledonous stems

A

transports water and mineral salts and provides a pathway from the roots to the rest of the plant

49
Q

What is the function of phloem in dicotyledonous stems

A

transports manufactured organic substances from the leaves to the rest of the plant

50
Q

What is the function of cambium in dicotyledonous stems

A

secondary thickening

51
Q

Why do dicotyledons have open vascular bundles

A

It has cambium and secondary growth can occur

52
Q

What do the secondary xylem and phloem develop from

A

fascicular cambium

53
Q

What is the fascicular cambium

A

The cambium found in the vascular bundles of dicotyledonous stalks, between the xylem and phloem

54
Q

What is interfascicular cambium

A

The layers of parenchyma cells in the medulla rays, between the vascular bundles in line with the fascicular cambium which are meristematic

55
Q

What occurs when the fascicular and interfascicular cambium are joined

A

A continuous ring of cambium tissue forms. Active cell division (mitosis) takes place in the cambium ring

56
Q

Where is secondary xylem and phloem formed

A

Secondary xylem is formed on the inside and secondary phloem form towards the outside of the cambium ring

57
Q

How often do new rings of secondary xylem and phloem form

A

yearly

58
Q

What happens when the secondary tissue is formed yearly

A

the primary xylem and phloem are pushed further apart

59
Q

What happens in places where the cambium does not form secondary xylem and phloem, but parenchyma cells instead

A

The parenchyma cells form the rays that extend from the middle of the stem and are known as pith rays. The pith rays are visible in the secondary xylem and phloem. The formation of the secondary tissue causes the stem circumference ti increase and become thicker

60
Q

Annual rings

A

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61
Q

Formation of cork

A

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Grade 10 Biology (9 decks)

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