SAT II Biology E/M Dr Haitham AbdAllah

0100 36 777 19

Plants
B. Kingdom Plantae

All plants are multicellular, eukaryotic, and photosynthetic (i.e., autotrophs) and
have cell wall made of cellulose

Plants are grouped into two general categories based on how they transport
water : nonvascular plants ( bryophytes ex: mosses) and vascular plants
(tracheophytes )

Vascular plants are further subdivided into seedless plants (ex ferns ) and seed
plants

Seed plants are further divided into nonflowering plants (gymnosperms) and
flowering plants (angiosperms)

monocot dicot

1) Division Bryophyta (Non-vascular Plants) ( no conducting tissue )

 Primitive plants
 lacks vascular tissue found in most plants, called xylem and phloem
 do NOT have true stems, leaves, and roots
 Must live in moist environment because they have no roots or xylem and
must absorb and transport water by OSMOSIS
 Bryophytes are tiny because they lack the lignin-fortified
tissue necessary to support tall plants in land

 Examples : mosses, liverworts, and hornworts mosses

ferns
2) Division Pterophyta (Ferns)
 Ferns are some of the earliest vascular plants and contain the
vascular tissue xylem and phloem ‫وظيفتها نقل الماء من التربة لبقية‬
‫ النبات و نقل السكر اللى اتعمل فى الورقة لباقي النبات‬as well as true stems,
leaves, and roots
 Do NOT have seeds. Instead, ferns have spores, which can be
scattered ‫ تحملها الرياح‬by wind

3) Division Coniferophyta (Conifers)

Plants
SAT II Biology E/M Dr Haitham AbdAllah
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 true vascular plants. The term conifer ‫ مخروطية‬refers to cones that carry
seeds of these plants

 Most are large evergreen trees such as pines‫ الصنوبر‬, fir ‫ نبات الشوح‬and cedar ‫األرز‬
Because seeds are not protected in a seed coat, these are “naked-seed” plants
( gymnosperms)
pines

 Gymnosperms do NOT produce flowers (nonflowering)

 They have various modifications to make seeds more resistant to

wind , cold , drought ‫ … جفاف‬these modific. Include : needle-
shaped leaves‫ مدببة زى االبرة‬, thick waxy cuticle and stomates
‫ ثغور‬to reduce water loss

 Ex : pines ‫ الصنوبر‬, sequoias , redwoods , yews , junipers

4) Division Anthophyta (Flowering Plants)

 True vascular plants that → produce flowers

 Angiosperms are flowering plants in which seeds develop inside
ovaries of flowers … they are the most diverse and plentiful plants on
earth

Examples are apples, lima beans, tomatoes, melons, Roses , daisies ,

fruits , nuts , grains , grasses

a) Class Monocots

 Monocots are named for their single seed leaves called cotyledons

Ex: grasses , wheat , corn , oats , lawn grass , rice ….. Monocots
provide food for most of the world….. palm trees are also monocots

b) Class Dicots

 Dicots have two seed leaves ( 2 cotyledons)

 Ex . of dicots : daisies , roses , carrots and most flowering plants
your could think of : Oak ‫ البلوط‬, walnut ‫عين الجمل‬, cherry ‫ الكرز‬and
most other trees your could name are dicots

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

Very important

A cladogram for plants ‫مهم جدااااا‬

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

shows evolutionary relationships among 4 main groups of living plants using the
prescence or absence of 3 derived traits : vascular tissue , seeds , flowers

Evolutionary developments that enabled plants to move to land :

Plants began life in seas and moved to land as competition for resources increased. The
biggest problems a plant on land faces are supporting plant body and absorbing and
conserving water. Several modifications enable plants to live on land

 Cell walls made of cellulose to support plant

 Roots and root hairs → absorb water and nutrients from soil
 Stomates ‫ ( ثغور‬in leaves ) open → to exchange photosynthetic gases ( O2 and
CO2 ) , close → to minimize excessive water loss
 Cutin ( Waxy ‫ شمع‬coating on leaves ) → helps prevent excess water loss from
leaves
 In some plants, gametes and zygotes form within a protective jacket of cells called
gametangia that prevents drying out
 Sporopollenin ( found in walls of spores and pollen ) → tough polymer ‫→ قوى‬
resistant to environmental damage and protects plants in harsh ‫ قاسي‬terrestrial
environment
 Seeds and pollen → have protective coat → prevents desiccation ‫… جفاف‬. They
are also means of dispersing offspring

 How plants grow

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

Unlike animals, plants continue to grow as long as they live because plants have
meristem tissue ‫ نسيج انشائي‬that continually divides , generating new cells . Plants
grow in two ways: primary growth
and secondary growth

1-Primary Growth

 Primary growth is vertical

 It is elongation of plant down into
soil and up into air

 New cells arise from growth layer

called apical meristem ( which is
located at buds of shoots and
root tips ) ( shoot and root
meristems )

 Root growth is concentrated near

root tip

 Three zones of cells at different stages of primary growth : → zone of cell

division called apical meristem , zone of elongation, zone of
differentiation

 Root cap protects root tip → (it secretes a substance that helps digest earth
‫ حواليها فى التربة‬as root tip grows through soil )

 Zone of cell division → Contains meristem cells → responsible for producing

new cells that grow down into soil … This is the region you observed under
microscope in lab when you were studying cells undergoing mitosis

 Zone of elongation → Cells here elongate to push ‫ تدفع‬root cap downward and
deeper into soil

 Zone of differentiation → Cells undergo specialization into 3 primary

meristems → that give rise to → 3 tissues : Dermal, Vascular ( xylem and
phloem ) , ground tissues

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

2-Secondary Growth ( By Lateral meristem )

Vascular Cork Cambium

Cambium

Secondary growth is lateral growth ( horizontal ) ‫ أفقى‬or increase in girth ‫ العرض‬..New

cells arise by lateral meristem

 In herbaceous (nonwoody) plants as vegetables and flowers → only primary

growth because these plants live for only one season

 woody plants are protected by bark ‫ اللحاء‬and live for many years.

 In these plants, secondary growth is responsible for enlargement of trunk

‫ كبرجذع الشجرة‬For each year of growth, another ring is added ‫حلقة جديدة بتضاف حول‬
‫جذع الشجرة فيزيد سمكها و ممكن نحدد عمرها بعدد الحلقات‬

Plants can live for hundreds of years as long as the meristem keeps dividing

‫ هام‬Branches donnot increase in width

Roots

Function → absorb nutrients from soil , anchor ‫ يثبت‬the plant and store food

Structure :

1-Epidermis

 Covers entire surface of root and modified for absorption

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

 Root hairs → Slender cytoplasmic projections ‫ زوائد رقيقة‬from

epidermal cells ‫ بتاعة الروووت‬extend out from each cell and increase
root’s absorptive surface area

2-Cortex ‫القشرة‬

 Function → storage
 consists of parenchyma cells
that contain many plastids for
storage of starch and other
organic substances

3- Stele ( vascular cylinder )

 Function → transport
 consists of vascular tissues
(xylem and phloem) surrounded by one or more layers of tissue
called the pericycle→ from which lateral roots arise

4-Endoderm

 Function → select what minerals enter stele ( vascular cylinder) and

body of plant
 Stele (Vascular cylinder) is surrounded by tightly packed layer of cells
called endodermis

 Each endoderm cell is wrapped with the Casparian strip → a

continuous band of waxy ‫ شمعية‬material that prevents water and
dissolved minerals from leaking back out to cortex ‫مايخليهمش يرجعوا لورا‬
‫ (تانى‬impervious)

Absorption of Nutrients and Water

Plants use their roots to absorb nutrients and water from soil …… These then
must be absorbed by the cells themselves

Symplast and Apoplast

 lateral movement ‫ → حركة جانبية‬movement of water and solutes across

plant → is accomplished by symplast and apoplast

 Symplast → a continuous system of cytoplasm of cells interconnected by

plasmodesmata ‫خيوط بالزموديزماتا‬

Plants
SAT II Biology E/M Dr Haitham AbdAllah
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 Apoplast →the network of cell walls and intercellular spaces ‫الفراغات بين‬
‫ الخاليا و بعضها‬within a plant body that permits extensive extracellular
movement ‫ حوالين الخاليا مش جواها‬of water within a plant

* Mycorrhizae (fungi ‫هام جدا) نوع من ال‬

 Mycorrhizae → symbiotic structures consisting of plant’s

roots intermingled ‫ متداخل‬with the hyphae (filaments) of a
fungus ‫ فطر‬that greatly increase quantity of nutrients the
plant can absorb

 In mature plants that lack root hairs ‫عشان مفيهاش‬

 supply plant with water and minerals

*Rhizobium ( bacteria ‫) نوع من الباكتيريا‬

 Rhizobium → symbiotic bacterium that lives in nodules on roots of legumes

‫البقوليات‬
 It fixes nitrogen gas from air into ammonium ( NH4 + ) ( form of nitrogen
the plant requires) ‫ ( هام جدا جدا‬nitrogen fixing bacteria ) ( see nitrogen cycle
ecology ch : )

Question : Leguminous plants such as soy beans and peas exhibit a mutualistic symbiosis with
(A) Herbivores
(B) Bacteria
(C) Other leguminous plants
(D) Humans
(E) Soils
Ans: B

Types of Roots

 Taproot → In dicots
 Some taproots “tap” water deep in soil ….. Others
like carrots , beets and turnips ‫ اللفت‬are modified for
storage

 fibrous root→ monocots like grasses, holds plant

firmly in place
 As a result, grasses make fine ground cover ‫عشب خفيف‬
because they minimize soil erosion

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

 Adventitious roots → roots that arise above ground ex :

1. Aerial roots :

Ex: English ivy ‫ اوراق اللبالب‬has aerial roots that enable ivy to cling
‫ تثبت‬to sides of buildings

Ex 2 : mangroves : Trees that grow in swamps ‫ مستنقعات‬or salt

marshes like mangroves have aerial roots that stick up out of water
and serve to aerate ‫ تهوى‬root cell

2. Prop Roots :

Ex : corn roots ‫ جذور نبات الذرة‬Some

tall plants have prop roots that grow
above ground out from base of
stem and help support plant

2-Leaf

leaf is organized to maximize sugar production while minimizing water loss

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

Stomates

 When plant cells carry out cellular respiration, they take in oxygen and give
off carbon dioxide
 When plant cells carry out photosynthesis , they take in carbon dioxide and
give off oxygen and water vapor

 Plants exchange these gases between air spaces in spongy mesophyll and the
exterior of the leaf by opening their stomates

 So why do plants ever close their stomates? If stomates were kept open all the
time, the plant would lose so much water through transpiration (loss of water
from the leaf) it could not survive

 To minimize excessive water loss, when the sun is shining brightly and
photosynthesis is running at top speed, stomates are open. At night, though,
most plants close their stomates
 Plants must keep their stomates open long enough to allow photosynthesis to
take place but not so long that they lose too much water

 Guard cells are modified epithelial cells that control opening and closing of
stomates in response to changes in water pressure
 When guard cells absorb water by osmosis and become turgid ‫ ( منتفخة‬rigid) ,
they curve like hot dogs, causing stomate to open
 When guard cells lose water and become flaccid, the stomate closes

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

3-Stems

 function support
 This support allows leaves to receive the most light
 Stems also → transport water and minerals from soil, and food from leaves to
the rest of plant

Structure
 Vascular tissue runs the length of the stem‫ بطول الساق‬in strands called
vascular bundles ( veins )
 Each bundle contains → xylem on the inside, phloem on the outside, and
meristem tissue between the two
 In monocots → vascular bundles are scattered throughout the stem
 In dicots → they are arranged in a ring around the edge of the stem
 The ground tissue of stem consists of cortex and pith ‫ القشرة و النخاع‬,
parenchymal tissues modified for storage

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

Types of plant tissues

 Just as there are different cell and tissue types in animals, plants too have
different cell and tissue types
 Plants consist of three main tissue types: dermal, vascular, and ground
tissue. A fourth tissue type, meristem tissue or growth tissue, is found
only in the growing tips of shoots and roots. It is also discussed in the
section, “How Plants Grow.”

Dermal Tissue

 Dermal tissue is outer protective covering of plants and usually consists

of single layer of epidermal cells
 On leaves, epidermal cells are protected by cuticle, which is made of
waxy molecule cutin

 Some leaves are covered with tiny, spikelike projections called

trichomes, which also protect the leaf

 For the most part, epidermal cells do not contain chloroplasts and
cannot photosynthesize

 Exception are guard cells which are modified epidermal cells that
contain chloroplasts and can photosynthesize ‫هام‬

Vascular Tissue ( conducting tissue )

 Vascular tissue → transports water and nutrients up and down the plant
 There are two types: xylem ( transports water ) and phloem ( transports
food/sugar )

sieve tube companion

 Xylem consists of tracheids and vessel elements elements cells

‫ اللى اتعمل فى ال‬food ‫ او ال‬sugar ‫ بينقل ال‬phloem ‫ و ال‬water ‫ بينقل ال‬xylem ‫ال‬
‫ لباقي النبات‬leaves
Ground Tissue
 It consists of 3 cell types: parenchyma, collenchyma, and sclerenchyma
cells
 Ground tissue makes up all plant tissue besides dermal and vascular
tissue ‫قلناهم فوق‬

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

 Parenchyma cells :

 traditional-looking plant cell , have primary cell wall that is

thin and flexible, and no secondary cell wall

 The cytoplasm contains one or two large vacuoles

 When cell is turgid (swollen) with water, these cells (

prenchyma ) lend ‫ تعطى‬support to plant

 found in all parts of plant ( stem , root , mesophyll cells in leaf ,

epidermis in leaf , phloem )

Collenchyma cells

 have unevenly thickened primary cell

‫ مش متساوى‬and flexible walls , lack
secondary cell walls

 The “strings” of celery ‫ الكرفس‬consist of

collenchyma cells

Sclerenchyma cells ( for support )

 have very thick primary and secondary cell walls that are fortified ‫مقوى‬
‫ بالليجنين‬with lignin
 function support

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

Transport in plants
Just like animals, plants need to transport water, nutrients, and gases. Unlike animals, plants
do not have blood, arteries, or a heart to accomplish this. Instead, they have xylem and
phloem

Xylem
 consists of two types of elongated cells: tracheids and vessel elements
 The secondary cell walls of tracheids are hardened with lignin and function to
support plant and transport nutrients and water
 Xylem → ( wood )

 Xylem carries water and nutrients from soil up to the tallest leaves against gravity
with no expenditure ‫ دون استهالك للطاقة‬of energy. Instead, they are pulled up by a
combination of two phenomena: transpirational pull and cohesion tension

 Transpiration evaporation of water from leaves

 Cohesion ‫التماسك‬ water molecules are attracted to each other and stick
together

 The transpirational pull-cohesion tension theory states that : for each molecule of
water that evaporates from a leaf by transpiration, another molecule of water is
drawn in at the root to replace it. The absorption of sunlight drives transpiration by
causing water to evaporate from leaf

 Several factors affect the rate of transpiration and loss of water from
a leaf :

 High humidity transpiration, low humidity

Plants
 SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

 Wind can reduce humidity near stomates and thereby transpiration

 Increased light intensity ‫ قوة الضوء‬will increase photosynthesis, thereby
increasing both amount of water vapor to be transpired and rate of
transpiration
 Closing stomates stops transpiration

Phloem
 Phloem vessels are made of chains of two types of cells: sieve tube
elements and companion cells
 They carry sugar from photosynthetic leaves to rest of plant by a process
called translocation
 Sugar is stored in roots Unlike transport in the xylem, this process
requires energy

 Plant reproduction

Plants can reproduce both asexually and sexually.

Asexual Reproduction

 Plants can clone themselves or reproduce asexually by vegetative propagation. In

this process, a piece of the vegetative part of a plant, the root, stem, or leaf,
produces an entirely new plant genetically identical to the parent plant
 Examples are grafting, cuttings, bulbs, and runners

Sexual Reproduction ( Flower is the reproductive organ of the plant )

1. Petals → Brightly colored, modified leaves found just inside the circle of
sepals; attract animals that will pollinate the plant

2. Sepals →Outermost circle of leaves; are green and closely resemble ordinary
leaves

3. Pistils or Carpels → Female part of the flower; produce the female

gametophytes; each consists of an ovary, stigma, and style

4. Ovary → Swollen part of pistil that contains the ovule, where one or more ova
are produced by meiosis

5. Ovule → The structure within the ovary where the ova (female gametophytes)
are produced

Plants
 SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

6. Style → Long, usually thin stalk of the pistil

7. Stigma → Sticky top of the style where pollen lands and germinates

8. Stamen → Male part of the flower, made up of anther and filament

9. Anther → Male part of the flower where sperm (pollen) are produced by meiosis

10. Filament → Threadlike ‫ شبه الخيط‬structure → supports anther

Pollination and fertilization in flowering plants

 Sexual reproduction begins with pollination ‫التلقيح‬

 One pollen grain containing 3 haploid nuclei — one tube nucleus and
two sperm nuclei— lands on sticky stigma of the flower

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

N.B :

- Pollen is made from little cells called microspores, and mature pollen
grains contain a cell that can divide to form → two sperm cells

-Inside ovary is the ovule, which forms cells called megaspores,

Megaspores can divide to form eggs and polar bodies

1) pollen grain absorbs moisture and germinates or sprouts ‫ تتبرعم‬producing

pollen tube that burrows down the style into → ovary

2) two sperm nuclei travel down pollen tube into ovary

3) Once inside the ovary, the two sperm nuclei enter the ovule through
micropyle
4) One sperm nucleus fertilizes egg and becomes →embryo (2n)
5) The other sperm nucleus fertilizes two polar bodies and becomes →
triploid (3n) endosperm or cotyledon (food for growing embryo )

6) This process is known as double fertilization because two fertilizations

occur

7) After fertilization :
ovule becomes seed and the ripened ovary becomes fruit ‫هام جدا‬

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

8) In monocots → food reserves remain in endosperm

9) In dicots → food reserves of the endosperm are transported to cotyledons,
and, the mature dicot seed lacks endosperm

In the monocot the coconut → endosperm is liquid

Double fertilization:

1. Sperm + Ovum → Embryo = 2n

2. Sperm + 2 Polar bodies → Cotyledon (Food for growing embryo)
= 3n

The seed

o Seed consists of protective seed coat, an

embryo, and the cotyledon or endosperm (
food for growing embryo )
o embryo consists of : hypocotyl, epicotyl,
and radicle

o hypocotyl becomes → lower part of stem and

roots

o epicotyl becomes → upper part of stem

o Radicle, or embryonic root, is first organ to

emerge from germinating seed ‫البذرة اللى بتنبت‬

o Figure 13.8 shows a dicot seed (like a peanut ‫ الفول السودانى‬split ‫ مقسومة‬in half

o A monocot seed, like corn, does not split in half

o Food source in monocot is endosperm instead of cotyledon

Alternation of generations

 The sexual life cycle of plants is characterized by alternation of generations in

which haploid (n) and diploid (2n) generations alternate with each other

Plants
SAT II Biology E/M Dr Haitham AbdAllah
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 gametophyte (n) produces →gametes by mitosis that fuse during

fertilization to → yield zygotes
 Each zygote develops into a → sporophyte (2n) that produces →haploid
spores (n) by meiosis
 Each haploid spore forms gametophyte, and cycle continues

Remember

The gametophyte generation is haploid (n)

The sporophyte generation is diploid (2n)

Term Definition
Antheridium Structure that produces sperm

Archegonium Structure that produces eggs

Gametophyte haploid ( n ) adult plant

Sporophyte Diploid (2n ) adult plant

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

Sporangia Located on tip of mature sporophyte, where

meiosis occurs → producing (n) spores

Protonema Branching, one-celled-thick filaments

produced by germinating moss spores

Sori Raised spots located on underside of

sporophyte ferns ‫جيل الفيرن اللى بيطلع سبورز‬
,clusters of sporangia

Bryophytes ( Mosses )
o primitive
o green, carpet-like plants growing in damp forests, sometimes on fallen logs
o gametophyte generation dominates its life cycle ‫ → هو األساسي فى النبات ده‬This
means that the organism is haploid (n) for most of its life cycle, and sporophyte
(2n) is dependent on gametophyte
o gametophyte obtains nutrients by photosynthesis
o sporophyte obtains nutrients from gametophyte

Ferns
o seedless vascular plant
o Sporophyte generation is larger and is independent ‫ مستقل‬from gametophyte
o Both gametophyte and sporophyte sustain themselves by photosynthesis

Seed Plants
o Seed plants are advanced, vascular plants
o divided into : Conifers ( cone –bearing ) ( gymnosperms ) and
flowering plants ( angiosperms )
o In gymnosperm (cone-bearing plant) like pine tree →
gametophyte generation develops from haploid spores ( retained
within the sporangia )
o In flowering plants (angiosperms) → gametophyte generation
is dependent on sporophyte

Plant hormones

Auxins ( the most important )

 First plant hormone to be discovered

Plants
SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

 Auxins → enhance apical dominance ‫نمو النبات لفوق‬

 stimulate stem elongation and growth by softening cell wall
 Indoleacetic acid (IAA) is a naturally occurring auxin

 A human-made auxin, 2,4-D , is used as weed killer ‫حشائش ضارة‬

 Auxins are used as rooting powder to develop roots quickly in plant cutting
 synthetic ‫ صناعى‬auxin sprayed on tomato plants will induce fruit production
without pollination → resulting in seedless tomatoes

Cytokinins

 stimulate cytokinesis ( division of cytoplasm ) and cell division ( see

cell division chapter )
 They delay senescence (aging) ‫ الشيخوخة‬by inhibiting protein
breakdown
 (Florists spray cut flowers with cytokinins to keep them fresh)

Gibberellins

 Gibberellins → promote stem and leaf elongation

Abscisic acid ( ABA )

 inhibits growth and promotes seed dormancy ‫خمول‬

 enables plants to withstand drought ‫ → يتحمل الجفاف‬closes stomates during
times of water stress

Ethylene ( enhances ripening ‫) النضوج‬

 is a gas → Ethylene gas promotes ripening ‫ النضوج‬which in turn → triggers

increased production of ethylene “One bad apple spoils the whole barrel.”
This is example of +ve feedback
 Commercial fruit sellers pick perishable fruit ‫ هالك‬before they are ripe while
still hard
 When fruit arrive at their destination → they are sprayed with ethylene to
hasten ‫ يسرع‬ripening
 In contrast, apples are kept in an environment of CO2 to eliminate
exposure to ethylene gas and keep apples from ripening or rotting ‫ تعفن‬so
apples can be stored for long periods of time

Tropisms ‫هام جدا‬

Plants
 SAT II Biology E/M Dr Haitham AbdAllah
0100 36 777 19

Tropism is growth of plant toward or away from stimulus ‫مؤثر‬

 Thigmotropism → plant response to touch

 Gravitropism ( geotropism ) → plant responds to gravity ( + ve → grow

downward ) , ( -ve ) → upward

 Phototropisms → plant responds (grows ) towards light ,

Phototropisms result from unequal distribution of auxins that
accumulate on the side of plant away from light

 Photoperiodism→ plant response to change In day length

 Phototaxis ex : When moths ‫ الفراشات‬moves towards light

 Chemotaxis ex : When mosquitos moves away from repellent

‫طارد للحشرات‬
-ve gravitropism

Plants