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BIOLOGY 3201

REPRODUCTION

Asexual vs. Sexual Reproduction

MODES OF REPRODUCTION

(1) Asexual – one parent cell divides into two by

mitosis to produce 2 identical cells which are

clones of the parent

(2) Sexual – new offspring are created as a result

of the fusion of an egg and sperm. The offspring

resemble but are not identical to the parents

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ASEXUAL REPRODUCTION

Asexual reproduction can be

advantageous when animals remain in

one particular place

Asexual reproduction results in

numerous offspring that can be

produced without "costing" the parent

a great amount of energy

Asexual reproduction is good where

environments that are stable

TYPES OF ASEXUAL REPRODUCTION

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1. BUDDING

offspring develop as a growth on the body of the

parent

examples:

cnidarians

yeast

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2. FRAGMENTATION

spontaneously break up into pieces. Each piece

develops into a mature organism

examples: flatworms, various fungi

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3. REGENERATION (FRAGMENTATION)

dividing and re-growing missing parts. They also

have the ability to regenerate injured body parts

examples: some invertebrates such as

Echinoderms (starfish), Planaria

Planaria

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4. BINARY FISSION

parent cell splits in half producing two identical

cells

most unicellular organisms

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5. PARTHENOGENESIS

"virgin birth"

females produce eggs, but these develop into young

without ever being fertilized.

some fishes, several kinds of insects, and a few

species of lizards

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IN HONEYBEES….

fertilized eggs (diploid) become females;

unfertilized (haploid) eggs become males

The queen controls the sex of her offspring. When an egg

passes from her ovary to her oviduct, the queen determines

whether the egg is fertilized with sperm from the

spermatheca. A fertilized egg develops into a female honey

bee, either worker or queen, and an unfertilized egg

becomes a male honey bee, or drone.

BIOLOGY 3201

UNIT 2:

REPRODUCTION

Seed Plants

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PLANT REPRODUCTION

Plants experience two distinct generations during their

life cycle

Sporophyte generation – produces spores (asexual by

mitosis)

Gametophyte generation – produces gametes (sexual

by meiosis)

However, angiosperms (flowering plants) do not use

any asexual reproduction; the sporophyte generation

doesn’t produce spores at all. As well, the gametophyte

generation is reduced to pollen grains and ovum cells

SEED

PLANTS

• Most

abundant

• Sporophyte

generation

predominant

• gametophyte

gen reduced to

sex cells

• Reproductive

organs -

flowers

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FLOWERS

Diploid

Perfect - both male and female sex organs

Imperfect - male or female flower

FLOWERS

CON’T

Pistil/Carpel -

female

Stamen - male

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FLOWERING STRUCTURES IN ANGIOSPERMS:

(1) pistil – a carpel or a group of fused carpels forming

the female reproductive part of a flower and including

the ovary, style, and stigma

ovary – swollen base of the carpel that contains ovules

style – stalk that connects the stigma to the ovary

stigma – sticky “lip” of the carpel that captures pollen

grains

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FLOWERING STRUCTURES IN ANGIOSPERMS:

(2) stamen – pollen-producing reproductive organ of a

flower, consisting of a filament and an anther

filament – the stalk which supports the anther

anther – top part of the stamen; produces pollen

(3) pollen – fine powdery material consisting of pollen

grains (microspores of seed plants, containing male

gametophytes) produced by anthers. It is carried by

wind and insects to other flowers which it fertilizes.

FLOWERING STRUCTURES IN ANGIOSPERMS:

(4) ovules – tiny structures in a seed plant, containing

the embryonic sac and surrounded by the nucellus that

develop into seeds after fertilization

(5) seed – reproductive structure of plants made up of

an embryo, stored food (endosperm) and a tough

waterproof coat

(6) fruit – structure formed by the ovary tissue of a

flower

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POLLEN PRODUCTION

1. Diploid cells in

the anther undergo

meiosis to produce 4

monoploid

microspores.

2. Each monoploid

nucleus divides by

mitosis to produce 2

monoploid nuclei -

the tube nucleus and

the generative

nucleus.

3. The outer wall

of the microspore

hardens forming a

pollen grain.

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EGG

PRODUCTI

ON

1. In the ovules diploid cells undergo meiosis to

produce 4 monoploid cells on which only one

survives.

The surviving cell is the megaspore.

2. Megaspore divides 3 times by mitosis to form 8

nuclei - two are polar nuclei , one is the true egg,

and five die.

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FERTILIZATION IN

FLOWERING PLANTS

1. Pollen sticks to

the stigma

2. A pollen tube

forms from the

tube nucleus.

3. Pollen tube enters

the ovule through

the micropyle.

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4. Generative

nucleus divides

by mitosis to

form two sperm

nuclei

5. Sperm nuclei

enter the ovule.

6. One sperm - joins 2 polar nuclei form the

triploid (3n) endosperm

7. One sperm - joins the egg - fertilization

producing a diploid zygote.

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FLOWERING

PLANTS

Fruit and Seed Formation

STEPS...

1. Endosperm nucleus divides to become the

endosperm.

2. Out covering of ovule hardens into the seed coat.

3. Ovary enlarges to become the fruit.

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Strawberry Flower

Developing Fruit