Morfologi Biji

110/8/2010 [email protected]

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Reproduksi

Seksual pd

Angiospermae


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Alat Reproduksi Angiospermae

Stamen / Benang Sari Setiap stamen terdiri atas anthera, yang mengandung

mikrosporangia dan didukung oleh filament

Meiosis pada sel induk mikrospora yang diploid di dalam antera menghasilkan empat mikrospora haploid.

Masing masing mikrospora akan berkembang menjadi serbuk sari dengan dua sel, kedua sel tersebut adalah :

Sel buluh serbuk dan Sel generatif

Karpel Karpel terdiri atas stigma, stylus dan ovarium. Semua bagian ini

membentuk pistilum.

The megasporangia, disebut ovul, berkembang di dalam ovarium. Meiosis pada sel induk megaspora di dalam setiap ovul

menghasilkan 4 sel haploid : 1 sel megaspora yang besar, dan 3 sel kecil yang disintegrasi.


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Development of the megaspore

The nucleus of the megaspore undergoes 3 successive mitotic divisions. The 8 nuclei that result are distributed and partitioned off by cell walls to form the embryo sac. This is the mature female gametophyte generation.

The egg cell will start the new sporophyte generation if it is fertilized.

The large central cell, which in most angiosperms contains two polar nuclei, will after its fertilization develop into the endosperm of the seed.


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Pollinasi

When a pollen grain reaches the stigma, it germinates into a pollen tube. The generative nucleus divides by mitosis forming 2 sperm nuclei. These, along with the tube nucleus, migrate down the pollen tube as it grows through the style and into the ovule chamber. The pollen tube with its contents makes up the mature male gametophyte generation.


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Double Fertilization

The pollen tube enters the ovule through the micropyle and ruptures.

One sperm nucleus fuses with the egg forming the diploid zygote.

The other sperm nucleus fuses with the polar nuclei forming the endosperm nucleus. Most angiosperms have two polar nuclei so the endosperm is triploid (3n).

The tube nucleus disintegrates.


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Ovum (n)

Penyerbukan

Zygota (2n)

:

Antipoda (n)

Inti kandungLembaga skunder (2n)

Inti kandungLembaga skunder (2n)

Sperma II (n)

Sperma I (n)

Embryo (2n)

Buluh serbuk

Serbuk sari

Benang sari

Sel kandung lembaga

Bakal biji

Putik

Bunga

Endosperm (3n)

Gambar 3 : Pembuahan ganda


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Buah (hasil pembuahan) Buah partenokarpi

Bakal biji

Ovum x sperma Ovarium Buah tak berbiji

Zygota Giberelin

(dihasilkan bakal biji yang tak dibuahi)

Embryo

Menghasilkan

Giberelin

Ovarium Buah berbiji


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FISIOLOGI

BIJI


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Biji

Mengandung embrio tumbuhan yang sedang berkembang dalam selubung protektif yang disebut testa

Biji terbentuk dari bakal biji (ovula) yang dibuahi di dalam ovarium

Ovarium dengan biji di dalamnya akan menjadi buah.


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After double fertilization, each ovule develops into a seed, which consists of

a plumule, made up of two embryonic leaves, which will become the first true leaves of the

seedling, and

a terminal (apical) bud. The terminal bud contains the meristem at which later growth of the stem takes place.

One or two cotyledons which store food that will be used by the germinating seedling.

Angiosperms that produce seeds with two cotyledons are called dicots. Examples: beans, squashes, Arabidopsis

Angiosperms whose seeds contain only a single cotyledon are monocots. Examples: corn and other grasses.

The hypocotyl and radicle, which will grow into the part of the stem below the first node ("hypocotyl" = below the cotyledons) and primary root respectively.

A pair of protective seed coats derived from the walls of he ovule.


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The food in the cotyledons is derived from the endosperm which, in turn, received it from the parent sporophyte. In many angiosperms (e.g., beans), when the seeds are mature, the endosperm has been totally consumed and its food transferred to the cotyledons. In others (some dicots and all monocots), the endosperm persists in the mature seed.

The seed is thus a dormant embryo sporophyte with stored food and protective coats. Its two functions are dispersal of the species to new locations (aided in angiosperms

by the fruit)

survival of the species during unfavorable climatic periods (e.g., winter). "Annual" plants (e.g., beans, cereal grains, many weeds) can survive freezing only as seeds. When the parents die in the fall, the seeds remain alive - though dormant- over the winter. When conditions are once more favorable, germination occurs and a new generation of plants develops.


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Seed:

Seed Coat

Embryo

Storage Tissue (Endosperm)

Seed Hormones

CK-CytoKinin

cell division

GA-Gibberellic Acid

cell expansion

AbA-Abscisic Acid

dormancy


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The Three Fundamental Parts

of a Seed

1. Seed Coat

2. Embryo

3. Storage

Tissue

1. Leaf

2. Stem

3. Root

of an Embryo


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Parts of a Seed External seed coat or testa Developing plant embryo Stored food called endosperm Seeds may be in one part (monocot)

or two parts (dicots)

MONOCOT

DICOT


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Parts of a Seed


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Gymnosperm Seed

A single fertilization produces the diploid (2n) embryo

The food source is the haploid megagametophyte

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Dicot vs. monocot seed

Dicot has two cotyledons (like bean)

Endosperm (food) is kept in the cotyledon

Monocot has one cotyledon which

absorbs the endosperm

tissue during

germination (corn)


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Kulit buah bersatu dengan kulit biji

Posisi Endosperm

Posisi embryo

Biji utuh

Kulit biji

mikropil

hilum

Biji utuh

endosperm

endosperm

remains of style

Kulit buah dan kulit biji yg bersatu

coleoptil

plumula

radikula

coleorhiza

A. Irisan membujur

radikula

plumula

kotyledon

A. Irisan membujur

embryo

Gambar 5. Struktur BijiA. Biji jagung

B. Biji kacang kedelai

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Growth of the shoot

Photosynthesis and Storage

Lifting the shoot above the soil

Producing lateral roots

Penetrating the soil

These functions. occur in this part of the embryo

Shoot apex

Cotyledon (leaf)

Hypocotyl (stem)

Radicle (root)

Root apex


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23http://www.biologie.uni-hamburg.de/b-online/ibc99/koning/seedgerm.html


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PENYEBARAN

BIJI

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Fruits serve many functions

in the plant world

Food source for the germinating seedling

Plants need to get around. They do this with their fruits.

Adaptations for dispersal


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Fruit and Seed Dispersal

The main function of the fruit is to disperse the seeds

Dispersal is important because 1. It spreads the progeny in order to

colonize new environments

2. Reduces competition for resources with parents

3. Reduces the chances of predators destroying all of the plants yearly seed production

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Types of Seed Dispersal

Three types of seed dispersal:

1. Self dispersal

Mechanical Ejection of Seeds

2. Physical Carrier Dispersal

Wind dispersal

Water dispersal

3. Biological Carrier Dispersal

Animal dispersal


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A. Self dispersal

Plants disperse their seeds by forceful ejection explosive fruits!

Witch hazel, squirting cucumber (jet propulsion)

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Mechanical

Ejection Geranium fruit

exploding

Legume

(Pea seeds)

A

combination

of ejection

and

attraction


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Mechanical

Ejection

Impatiens Fruit Exploding

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Self dispersal The peanut plant sows

(buries) its own seeds!

Geocarpic: carpel grows inside the earth (soil)


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B. Wind dispersal Small and Lightweight seeds.

Fruit and seeds may have special devices for wind dispersal

Plumes catch wind currents: Dandelion

Trees take advantage of their great heights for wind dispersal. Fruits with wings are used to slow the descent to land: maple, ash fruit

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C. Water Dispersal Fruits and/or seeds use flotation

devices to travel by water (in rivers,

oceans, etc.)

Fruit may have air spaces and corky floats: for example coconut


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Coconuts are Water Dispersed


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D. Animal dispersal Plants have interaction with animals to

accomplish seed dispersal

Many plants depend on animals for seed dispersal; they may offer a nutritional reward

Animals learn to recognize ripened fruit colors

Fleshy fruits eaten and dispersed with feces

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Animal dispersal Some dry fruit attach and cling to

animals

(they hitchhike on the animals)

Some have Velcro-like hooks that cling to animal fur (burdock, cockleburs)

Others have sticky substances that stick to host (mistletoe)

Oils attract ants.


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Animal Dispersal

Long distance dispersal by birds:

fruits and seeds trapped in the mud on their feet

Seeds released in excrement

Animals eat fruit, the seeds pass through the digestive tract.

Scarification by digestive enzymes is necessary for germination

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How Ripened Fruits

Attract Animals

1. Softer, easier to digest

2. More fragrant

3. Brightly colored

4. Increase in sugar content is a source of carbohydrates (reward)

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Further Study on Seed

Dispersal What carries the dandelion seeds for miles?

What feature of trees gives them a particular advantage when dispersing seeds by air?

How does the squirting cucumber disperse its seeds?

Although plants use wind and water, what do most plants use as carriers for their seeds?

Blackberries on a tree do not ripen simultaneously, why?

What plant do elephants help to disperse? How do they do it? What percentage of these seeds

germinate in elephant dung? Why?


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Pithecellobium oblongum fruit shows some of the traits often found in the

fruits of bird-dispersed seeds

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Fruits and Dispersal Fruits remain

distasteful to most animals (including humans) until they are ripe

This ensures that the fruit will not be eaten until the seeds are mature

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