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NEET BIOLOGY > AOFP 1 > Flashcards

AOFP 1 Flashcards

1
Q

what is a tissue

A

Tissue : A group of cells having a common origin and usually
perform a common function.

  • Meristematic tissue- do not have any specialised function/ divides continually/ immature cells
  • Permanent tissue- mature cells/ do not divide/ have a specific function
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2
Q

describe the general features of meristematic tissue

A

Meristem : Growth in plants is largely restricted to specialised
regions of active cell division called meristems.

*Characteristics-
*Undifferentiated
*Primary cell wall present (Cellulosic) (SCW absent)
*Plasmodesmata present
*Cells isodiametric
*Large nucleus, dense cytoplasm
*Metabolically highly active, reserve food absent Plastids, vacuole,
ergastic substances(non living storage substance/ substrate present in cytoplasm) and intercellular spaces absent.

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3
Q

classification of mertistem based on origin/ development

A

Promeristem—-Primary Meristem—-differentiaition–> Primary permenant tissue——dedifferentiation—-> Secondary meristematic tissue——redifferentiation—-> secondary permanent tissue

Primary meristem : Apical meristem, intercalary meristem,
Intrafascicular cambium
Secondary Meristem : Interfascicular cambium, cork cambium

Primary meristems are present in plants from early plant
developmental stages Involved in primary plant body formation
*Secondary meristems are originates after primary meristem,
Present in mature region of root and stem

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4
Q

clasiification of mertistem based on position:
apical meristem

A

Apical meristem : Primary meristem
Occurs at tip of root and shoot
Different part of apical meristem :
1.Protoderm : Outermost layer
Give rise to epidermis, stomata, stem hairs etc.
2. Ground meristem :
Give rise to ground tissue system (Hypodermis, general cortex,
endodermis, pericycle, pith rays and pith)
3. Procambium
Give rise to vascular tissue system (xylem and phloem)

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5
Q

clasiification of mertistem based on position:
intercalary meristem

A

Intercalary meristem : Primary meristem
Occurs between mature tissues.
●Present at the base of internodes of monocot stems e.g. Grass,
bamboo, sugarcane etc.
●At the base of leaves
●They occur in grasses and regenerate parts removed by the grazing
herbivores

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6
Q

classification of meeristem
: lateral meristem

A

Occurs on lateral side of plant organs.

-Primary Lateral Meristem
E.g. Marginal meristem,
Intrafascicular cambium

-Secondary Lateral Meristem
(Mostly)
(fascicular vascular cambium)
E.g. Dicot Stem : Interfascicular
cambium and cork cambium
E.g. Dicot Root : Vascular cambium
and cork cambium

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7
Q

Composition / Organisation of Apical Meristem in different plants

A

●Absent in most of algae and fungi
●In some algae (e.g. brown algae), bryophytes and some
pteridophytes, one meristematic cell is present at the apex.
●In ferns, gymnosperms and angiosperms apical meristems consist
of many cells.

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8
Q

what does histogen theory says

A

Histogen theory : Hanstein
Given for root and shoot apex.
Most valid theory for root apex organisation

Apical meristem has 3 parts:
Dermatogen
*Outermost
*single layer
*Forms epidermis.

Periblem
*Just below the dermatogen
*Forms cortex (Hypodermis,
General cortex and
endodermis)

Plerome
*Innermost histogen
*Forms pericycle, vascular
bundles, pith & pith rays.

In monocot root, root calyptrogen is present outside the dermatogen.

Root apical meristem is subterminal in position. It is covered by a root cap. Root cap is formed by dermatogen in dicot, but it is dormed by calyptrogen in monocot. ( root cap is present outside of calyptrogen)
Root cap is absent in hydrophytes

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9
Q

what is quiscent centre in histogen theory

A
  • Term coined by Clowes
  • Discovered in Maize root apex
  • A group of inactive or less active cells
  • Present between the dermatogen and calyptrogen of monocot root.
  • Cells contain less amount of DNA and RNA
  • Light cytoplasm, small nuclei
  • Crescentic shaped
    Function : Serves as a reserve for replenishment of damaged cells of the
    meristem.
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10
Q

what is tunica corpus

A

Tunica corpus theory : Schmidt
based on plane of division
aplicable for shoot meristem

TUNICA
Peripheral layer
Anticlinal division
Epidermis formation

CORPUS
Present below the tunica.
Division in all direction (all planes)
Formation of ground tissue system
and vascular tissue system.

Growth of leaf primordium : First apical then marginal.( first it grows to protect shott tip, later turns into flower/leaf etc)
*Function of leaf primordium : Provide protection to shoot apex.

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11
Q

what are axillary buds

A

*During the formation of leaves and elongation of stem, some cells “
Left behind “ from shoot apical meristem, constitute the axillary
bud.
*Such buds are present in the axils of leaves and are capable of
forming a branch or a flower.
*Root apical meristem occupies the tip of a root while shoot
apical meristem occupies the distant most region of the stem
axis.

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12
Q

what is permanent tissue

A

Permanent tissues are composed of cells which have lost the power of
division temporarily or permanently. They are formed by division and
differentiation of meristematic tissues. The cells of permanent tissues do
not generally divide further.
●Their cells may be living or dead.

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13
Q

classification of permanent tissue

A
  • simple/homogenous permanent tissue
  • parenchyma, collenchyma, scelerenchyma

Made up of only one type of cells (Homogenous)
Perform a common function

  • complex/ heterogenous permanent tissue
    -xylem,phlome

Made up of more than one types of cells
*Heterogenous tissue
*Absent in gametophytes

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14
Q

describe parenchyma

A
  1. Parenchyma (Grew) :
    First evolved
    Primitive type of tissue
    Fundamental tissue or precursor of other tissues
    Universal tissue

*Thin walled, pectocellulosic cell wall (mainly cellulosic).
*Closely packed or have intercellular spaces.
*It forms major component within organs.
*Found in cortex, pericycle, medullary rays, pith, leaf mesophyll etc.
*Body of bryophyte is parenchymatous
*Pulp of fruit is mainly parenchymatous

Shape : Parenchyma cells are generally isodiametric. They may be
spherical (rounded), oval, elongated or polygonal in shape.

Functions of parenchyma :
*Storage
*Photosynthesis
*Secretion
*Some cells of parenchyma store waste materials (oils, tannin and
crystals). They are called “idioblast cells“.

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15
Q

what are the modification of parenchyma

A

*Prosenchyma : Rod Shaped, Pericycle of roots

*Aerenchyma : Usually found in cortex region, Provide
buoyancy to hydrophytes

*Stellate parenchyma : Star shaped

*Chlorenchyma : Parenchyma cells with chloroplast.
Found in the mesophyll of leaves.
Perform photosynthesis.

*Mucilage Parenchyma : Present in Succulent (fleshy)
xerophytic plants
Aloe, Opuntia, Euphorbia
Function - storage of water

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16
Q

describe collenchyma

A

*Living mechanical tissue
*Localized deposition of pectin (mainly),
cellulose & hemicellulose occurs mainly at
corners
*Usually intercellular spaces are absent
*Assimilate food when they contain chloroplasts

It is made up of more or less elongated cells (In transverse
section cells appear oval, spherical / rounded or polygonal in
shape).

*Found in the aerial herbaceous dicot stem either as a homogenous
layer (in sunflower stem) or in patches (in Cucurbita stem) just
below to epidermis.
*At the margins of leaf lamina and petiole of leaves
*Absent in mature / woody plant parts
*Absent in monocot plant
*Absent in roots and underground plant parts

*Mechanical as well as biological / vital functions
*Provides tensile strength against bending & swaying (mechanical
function)
*Mechanical support to the growing parts of the plant such as young
stem and petiole of a leaf
*photosynthesis process (vital function)

17
Q

describe scelerenchyma

A

Dead mechanical tissue
*Cells are generally long, narrow, thick walled, lignified & without
protoplasts
*Present in hypodermis of monocot stem
*Various types of pits are formed
Function : It provides mechanical support / mechanical
strength to plant organs

types of sclerenchyma:
i) Sclereid
*Cells are small, dead extremely thick walled highly thickened
*Generally ends are not pointed
*Spherical, oval or cylindrical
*Have pits
*Lumen (cavity) is very small / very narrow
Occurrence :
*Fruit walls of nuts
*Pulp of guava, pear & sapota (Stone cells)
*Seed coats of legumes
*Leaves of tea etc.

  • Fibres
    *Thick walled, long elongated and pointed end cells.
    *Lumen is reduced
    *Occurs in group in various parts of the plant
    *Their cell wall contains pits
18
Q

xylem classification

A

xylem consits of:
- vessels
-tracheids
- xylem parencyma
-xylem fibres

all are dead except xylem parenchyma

there are 2 types:
Protoxylem- smaller vessel element
Metaxylem- larger vessel elements

19
Q

phloem classsification

A
  1. Sieve tube element
  2. Companion cell
  3. Phloem parenchyma
  4. Phloem fibre

all are living except phloeme fibres.

There are 2 types:
protophloem- smaller sieve tube- earlier formed primary phloem
metaphloem- larger sieve tube- later formed primary phloem

20
Q

explain xylem and its different elements

A

*The function of xylem is to conduct water & mineral salts upwards
from the roots to stem & leaves

*Give mechanical strength to plant parts( mainly has ded element)

*In hydrophytes xylem is poorly developed, while in xerophytes
xylem is well developed

TRACHEIDS
*Primitive sap conducting elements
*Dead elongated or tube like cell with tapering end
*Thick and lignified walls
*Narrow lumen
*Pitted end wall (Usually bordered pits)
*The inner layers of cell walls have thickenings which
vary in form
NOTE : Maximum bordered pits are present in xylem
tracheids of gymnosperms

VESSEL
*Advanced Sap conducting elements
*Present in most of angiosperms and few
gymnosperms
*Long cylindrical, tube like structure made up of
many vessels elements with lignified walls
*Broad central lumen / cavity
*Perforated end walls (Simple or Multiple)
*Dead syncyte

Xylem fibres / Wood fibre
*Septate or aseptate.
*Highly thickened walls and obliterated(highly diminished) central lumens
*Abundant in secondary xylem
*Generally not found in gymnosperm wood (Soft wood
spermatophyte)

Xylem parenchyma
*Cells living and thin walled
*Their cell walls are made up of cellulose
Function : Storage of food materials (starch or fat)
Storage of other substances like tannins
NOTE :
Ray parenchyma (Xylem ray) is involved in radial conduction of
water
Hadrome : Conducting element of xylem

21
Q

general intro to phloem

A

The main function of the phloem is to conduct/transport food material,
usually from the leaves to other parts of the plant.

  • Sieve tube elements, companion cells, phloem parenchyma & phloem
    fibres (In angiosperms).
  • Sieve cells, albuminous cells(strassburger cells), phloem parenchyma & phloem fibres (In gymnosperms).
22
Q

parts of phloem

A

SIEVE TUBE CELLS
*Sieve element was discovered by Hartig.
*In Angiosperm plants, sieve tube
elements are joined from their ends to
form sieve tube.
*Their end walls are perforated (means
having sieve pores) in a sieve like
manner to form the sieve plates
(oblique perforated septa).
* Sieve tube elements are long, tube like
structures arranged longitudinally and
are associated with companion cells.
*A mature sieve tube element possess
a peripheral cytoplasm & a large
vacuole but lacks a nucleus.
*The function of sieve tubes are controlled
by the nucleus of companion cells.

COMPANION CELLS
*These are thin walled, living, specialised
parenchymatous cells, which are closely
associated with sieve tube elements.
*The sieve tube elements and companion
cells are connected by pit fields present
in
their common longitudinal walls.
*The companion cells help in maintaining
the pressure gradient in the sieve tubes.

PHLOEM FIBRES / BAST FIBRES
✔Sclerenchymatous; pointed needle like
✔Generally not found in primary phloem
✔Provide mechanical support to sieve elements.

PHLOEM PARENCHYMA
✔ Storage of food material
✔ Function of phloem rays (ray parenchyma) is conduction of
food in radial direction.
✔ Phloem parenchyma is absent in most of the monocotyledons.

23
Q

longest plant cell

A

fibre

NEET BIOLOGY (32 decks)

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