1. Pollination & Fertilization
Seeds, Fruits and Embryos

2. Section One
Flowers

3. Flowers
Most people appreciate flowers for their appearance or their fragrance.
Why do plants have flowers? Think about it!
Flowers are the reproductive organs of certain plants. They are specialized to carry out sexual reproduction and to begin the development of fruit and seeds.
Let’s look closely at the structure of a typical flower.

4. Flower Structure
The receptacle is the structure at the tip of the twig. All the flower parts are attached to the receptacle.
The most visible parts of many flowers are the petals.
All the petals together form the corolla of the flower.
The petals usually are scented and brightly colored. This helps attract insects and animals, such as butterflies, bees and birds.

5. Flower Structure
The centrally located pistil is the female organ of the flower.
The pistil consists of the following parts:
Stigma – The sticky top.
Style – The slender stalk that supports the stigma.
Ovary – The swollen base that contains the ovules (immature seeds).

6. Flower Structure Each stamen consists of the following parts:
Anther – The sac-like structure at the top of the stamen that produces and stores pollen.
Filament – The slender stalk that supports the anther.
Sepals are the outermost circle of leaves that serve to protect the other parts of the flower while it is still a bud.
All the sepals together form the calyx of the flower.
Sepals are usually green in color, but they may be the same color as the petals.

7. Information A complete flower contains these parts:
Pistil
Stamens
Corolla (petals)
Calyx (sepals)
A flower that lacks any of these parts is an incomplete flower.
An incomplete flower that lacks a pistil is a staminate (male) flower.
An incomplete flower that lacks stamens is a pistillate (female) flower.

8. Review
In addition to a receptacle, complete flowers have these structures:
Pistil (female organ)
Stamens (male organs)
Corolla (petals)
Calyx (sepals)
An incomplete flower lacks one of the listed structures.
Staminate (male) flowers are incomplete because they lack pistils.
Pistillate (female) flowers are incomplete because they lack stamens.

9. Select The Best Matching Choice:
Staminate:
Answer Column:
A female flower organ
Lacking pistils
Flower petals
Lacking stamens
A male flower organ
Flower sepals
Lacking a receptacle
Lacking sepals
Correct Answer: B
Pistillate:
Correct Answer: D
Stamen:
Correct Answer: E
Pistil:
Correct Answer: A
Calyx:
Correct Answer: F
Corolla:
Correct Answer: C

10. Gametophytes and Pollination
Section Two
Gametophytes and Pollination

11. Information
Flowering plants reproduce sexually through the union of male and female gametophytes (gametes) during fertilization.
The male gametophyte is in the pollen (located in the anther).
The female gametophyte is the ovule (located in the ovary).
Pollination includes the transfer of pollen from an anther to a stigma. Before fertilization can take place in the ovary, pollination must occur.

12. Anthers The anther produces pollen.
The anther is located in an exposed position, making it easy for the wind or visiting animals to disperse the pollen.

13. Flowering Plant Gametophytes
Each anther has four pollen chambers, or sacs.
Within the pollen sac, diploid cells develop (change) into pollen grains.
A diploid cell contains 2N chromosomes (N pairs). The value of N is different for almost every species.
Each diploid cell divides twice by meiosis, forming four haploid microspores.

14. Flowering Plant Gametophytes
Haploid microspores contain half the chromosomes that the diploid cell contained.
Therefore, each microspore has 1N chromosomes.
Meiosis produces cells that each have a haploid (N) number of chromosomes.
Each microspore becomes a pollen grain.

15. Flowering Plant Gametophytes
A thick cell wall forms. This protects the grain and prevents it from drying out.
The nucleus divides by mitosis, producing two nuclei within each pollen grain.
One nucleus in the pollen grain is the tube nucleus.
The other nucleus is the generative nucleus.
Each pollen nucleus has 1N chromosomes. Mitosis produces two haploid (N) nuclei from the original haploid nucleus.

16. Flowering Plant Gametophytes
When the pollen sac matures and splits open, it releases thousands of pollen grains.
After being released from the anther, pollen is carried by the wind or animals and can find its way to the sticky stigma of the same or another flower.

17. Flowering Plant Gametophytes
The ovary produces ovules.
There can be several ovules within an ovary.
Each ovule is attached to the wall of the ovary by a short stalk.
Meiosis occurs twice in each ovule, forming four haploid cells, three of which disintegrate.
The haploid cell in the ovule has 1N chromosomes. Haploid cells contain half the number of chromosomes found in diploid cells.

18. Flowering Plant Gametophytes
The remaining haploid cell divides several times by mitosis to produce the embryo sac (female gametophyte).
The embryo sac contains seven cells, one much larger than the others, and two polar nuclei.
The polar nuclei can be fertilized by the pollen to form the endosperm (food) in the seed.
One of the smaller cells is the egg cell, which can be fertilized by the pollen to form a zygote.
Each nucleus in the embryo sac has 1N chromosomes. Mitosis preserves the chromosome number in each haploid nucleus.

19. Pollination
Pollination is the transfer of pollen from an anther to a stigma.
Self-pollination is the transfer of pollen from the anther to the stigma of the same flower or to the stigma of another flower on the same plant. Self-pollination requires both male (stamen) and female (pistil) parts on the same plant.
Only complete flowers, having both stamens and a pistil, can pollinate themselves.
Incomplete flowers on the same plant can pollinate each other only if one flower is pistillate and the other is staminate.
Cross-pollination is the transfer of pollen from an anther on one plant to a stigma on another plant of the same species.

20. Information
Many plants can fertilize themselves through self-pollination, but this is not an effective means of reshuffling genes within a species and increasing variety.
Cross-pollination is most effective in creating new combinations of genes within plants.
Cross-pollination is the transfer of pollen from an another to a stigma on another plant.

21. Review
The anthers of flowering plants produce male gametophytes called pollen.
Each pollen grain contains one tube nucleus and one generative nucleus. Both nuclei are haploid.
The ovary produces female gametophytes called embryo sacs.
An embryo sac contains seven cells (including one egg cell) and eight haploid nuclei.
Pollination is the transfer of pollen from an anther to a stigma and is an essential step in sexual reproduction among flowering plants.

22. Select The Letter Of The Correct Answer From The List Below:
A. diploid D. pollination
B. haploid E. ovary
C. seven F. pollen
The male gametophyte, ____________________, is formed in the anther.
The __________________ produces the female embryo sac.
Mature pollen and mature egg cells contain _________________ nuclei.
An essential step in sexual reproduction in flowering plants is ________________.

23. Answers: pollen ovary haploid pollination
The male gametophyte, ____________________, is formed in the anther.
The __________________ produces the female embryo sac.
Mature pollen and mature egg cells contain _________________ nuclei.
An essential step in sexual reproduction in flowering plants is ________________.
ovary
haploid
pollination

24. Fertilization and Embryos
Section Three
Fertilization and Embryos

25. What Happens After A Pollen Grain Lands On The Surface Of A Stigma?
Sticky fluid, hairs or rough projections often cover the stigma and hold the pollen grain.
Chemicals from the pistil cause the pollen grain to grow and form a pollen tube.
The generative nucleus divides by mitosis to form two haploid sperm nuclei.
The haploid tube nucleus controls the growth of the pollen tube.

26. What Happens After A Pollen Grain Lands On The Surface Of A Stigma?
The pollen tube continues to grow down through the pistil for several hours until it reaches the embryo sac in the ovary.
When the pollen tube reaches the ovule within the ovary, it digests a hole in the embryo sac wall.
Then, the tube nucleus disintegrates.
One sperm nucleus enters the embryo sac and fuses (unites) with the egg nucleus to form a zygote (fertilized egg).
This process is called fertilization.

27. What Happens After A Pollen Grain Lands On The Surface Of A Stigma?
The zygote is a diploid cell containing 2N chromosomes; N from the sperm and N from the egg.
The two haploid polar nuclei fuse to form a diploid fusion nucleus which, in turn, fuses with the other sperm nucleus.
This second fertilization results in an endosperm nucleus.
The endosperm nucleus has triploid (3N) chromosomes, three times the chromosome number of an egg or a sperm.

28. Information
The ovules of flowering plants undergo double fertilization:
One sperm nucleus from the pollen grain fertilizes the egg to form the zygote.
The other sperm nucleus fertilizes the polar nuclei to form the endosperm nucleus.
The zygote develops into an embryo, and the endosperm nucleus becomes the stored food that nourishes the embryo.
A seed is a matured ovule consisting of the embryo and its stored food.

29. Fertilization Summarized
The sperm and the egg are haploid cells, each containing N chromosomes.
Fusion occurs when the sperm and the egg nuclei combine to form a zygote.
The zygote nucleus is diploid and contains 2N chromosomes.
In flowering plants, a second fertilization takes place.
The two haploid polar nuclei (inside the embryo sac) combine to form a fusion nucleus.
The fusion nucleus is diploid and contains 2N chromosomes.
The second sperm nucleus then fuses with the fusion nucleus to form the endosperm nucleus.
The endosperm nucleus is triploid and contains 3N chromosomes.

30. Cell Division
The seed develops from the ovule as the zygote and endosperm nucleus undergo many cell divisions during the process of mitosis.
During mitosis, the nucleus divides and forms two nuclei identical to the original.
After the nucleus divides, the entire cell divides and two identical cells form.

31. What Happens To A Flower After Fertilization?
The flower’s job is done after fertilization. Much of the plant’s energy is used to develop the ovary and the ovules.
In several weeks, the fertilized ovule ripens and becomes a seed.
The ovary also ripens and becomes a fruit.
If an ovary contains several ovules, each ovule can form a seed.
The petals and stamens of the flower are no longer necessary, and they often wither.
In many plants, however, the receptacle and the calyx become part of the fruit.

32. Review
Under the control of the tube nucleus, the pollen tube grows down through the pistil until it reaches the ovule. Then, the two sperm nuclei enter the embryo sac.
Within the embryo sac, the haploid sperm nuclei carry out two separate fertilizations. One forms a diploid zygote (fertilized egg) and the other forms a triploid endosperm nucleus.
The zygote develops into an embryo (immature plant). The endosperm nucleus provides food (endosperm) for the growing embryo.
A seed is a mature ovule made up of an embryo and an endosperm.

33. Quiz: Fill In The Blanks…
After pollination, the tube nucleus directs the growth of the _____________ through the pistil to the ovule. The two haploid ___________ nuclei then enter the embryo sac. There, one nucleus combines with the egg nucleus to form the diploid ____________. The other nucleus combines with the fusion nucleus to form the triploid _____________ nucleus. Eventually, the cells that contain these nuclei, and the surrounding ovule, become a seed.
pollen tube
sperm
zygote
endosperm

34. Section Four
Seeds and Fruit

35. Fruits
A fruit is a ripened ovary that can include other parts of the flower, such as the calyx and the receptacle.
Most fruits can be classified as either fleshy or dry.
Fleshy fruits are soft and pulpy at maturity.
Let’s learn more about these types of fleshy fruits:
Apple
Grape
Peach

36. Apple
An apple is a pome type of fleshy fruit. Its outer fleshy layer is derived from the calyx and receptacle of the flower (blossom).
The soft core, formed from the ovary, contains several seeds.
A pear is another example of a pome.

37. Grape
A grape is a berry type of fleshy fruit. The fleshy layer, often juicy, is derived entirely from the ovary and contains numerous seeds.
Other examples of berry type fleshy fruits include the following:
Watermelon
Tomato
Banana

38. Peach
A peach is a drupe type of fleshy fruit. It consists of an outer fleshy layer and an inner hard and stony layer.
Both layers are formed from the ovary. The inner layer (pit) contains one or more seeds.
Other examples of drupe type of fleshy fruits include the following:
Plum
Cherry
Olive

39. Dry Fruit
Dry fruits are another kind of fruit with which you are probably familiar.
Dry fruits are dry and hard or papery at maturity.
Let’s learn more about these types of dry fruits:
Bean pod
Corn kernel
Acorn

40. Bean Pod
A lima bean plant produces a pod type of dry fruit. The fruit consists of a single chamber (pod) containing many seeds.
The pod splits when ripe and releases the seeds (beans).
Other examples of plants that produce pod type dry fruits include:
Pea plant
Milkweed plant
Lily plant

41. Corn Kernel
A corn kernel is a grain type of dry fruit. Each kernel (grain) of corn is a complete fruit.
A corn kernel contains one seed. The seed coat is permanently attached to the ovary wall.
Other examples of plants that produce grain type dry fruits include:
Wheat
Oat
Barley

42. Acorn
An acorn is a nut type of dry fruit. It consists of one seed surrounded by a hard ovary wall.
Other examples of nut type dry fruits include the following:
Hazelnut
Pecan
Chestnut

43. Information
A seed is the mature ovule of a flower, consisting of the following parts:
Seed coat
Embryo
Endosperm
The seed coat (outer layer) develops from the wall of the ovule and protects the embryo against injury, parasites and dehydration.
The embryo is a tiny plant that develops from the zygote.
The endosperm develops from the endosperm nucleus of the embryo sac. It provides the embryo with nutrients.

44. Monocot Seed Structure
A kernel of corn is a complete fruit.
Let’s examine the following parts of a corn kernel:
Cotyledon
Hypocotyl
Epicotyl
Endosperm

45. Monocot Seed Structure
Corn is a monocot plant. Each kernel has one cotyledon that contains stored nutrients (starch and sugar).
The cotyledon absorbs food from the endosperm when the kernel germinates.
The hypocotyl is the embryonic stem and root of the corn plant.
The rolled-up leaves of the epicotyl are true leaves that become permanent leaves in the adult plant.

46. Monocot Seed Structure
The endosperm fills most of the corn grain and contains starch and sugar.
The plant uses the endosperm as a source of food for growth.

47. Dicot Seed Structure Each lima bean is a separate seed.
Let’s examine the following parts of the bean seed embryo:
Cotyledons
Hypocotyl
Epicotyl

48. Dicot Seed Structure
The bean is a dicot plant. Bean seeds have two cotyledons.
The cotyledons completely digest and absorb the endosperm and make up most of the bean structure.
The cotyledons store a large amount of protein and starch. This provides food for the growing embryo as well as for humans and other animals that eat the bean.
The hypocotyl is the embryonic stem and root of the plant.
The epicotyl consists of two tiny leaves that grow quickly when the seed germinates (sprouts).
The leaves of the epicotyl are true leaves that become permanent leaves in the adult plant.

49. Information Seeds can be dispersed by the following means:
Mechanical
Wind
Animals
Water
Each plant’s seeds are specialized to take advantage of one method of seed dispersal.

50. Information
Mechanical dispersal occurs when a pod dries out and bursts. Seeds within the pod can be thrown several feet.
The wind carries dandelion and maple seeds, which contain wisps of hair or wings.
Animals help disperse seeds by eating fleshy fruits and eliminating the seeds in their feces. Seeds with burrs can stick to animal fur and be carried several miles.
Water helps disperse floating seeds or fruit, such as the coconut.

51. Seed Germination
Under favorable conditions, a seed can germinate (sprout) and form a new plant.
Let’s compare the germination of a monocot grain of corn and a dicot bean seed.

52. Monocot (Corn) Seed Germination
The embryo absorbs water, and the root pushes through the softened fruit to form a temporary primary root.
Growth occurs as cells divide mitotically in the embryo’s meristematic tissue.
The tightly rolled leaves of the epicotyl push through the soil and secondary branch roots develop.
Meristematic tissue continues to produce cells that become roots, stems and leaves.
Once above ground, the leaves unroll and the stem grows to form the cornstalk.
The hypocotyl and cotyledon of the corn grain never appear above ground.

53. Dicot (Bean) Seed Germination
Water softens the seed coat, and the hypocotyl grows out. Mitotic division of the cells making up the embryo’s meristematic tissue provide new cells for growth.
The root grows downward and the hypocotyl forms an arch that pushes up through the soil.
Above ground, the hypocotyl straightens and lifts up the two cotyledons and becomes the shoot.
The tiny leaves of the epicotyl unfold and grow into adult plant leaves.
A dicot’s hypocotyl and cotyledon appear above ground. A monocot’s hypocotyl and cotyledon remain below ground.

54. Information Several factors influence the germination of seeds:
Water
Air
Temperature
Light
Water is needed to soften the seed coat (allowing the embryo to grow) and aid in the life processes during growth. Too much water can cause rotting.
Seeds must have oxygen to convert food into the energy required for rapid cell division and growth.
The two most important factors that affect seed germination are moisture and warmth.

55. Review
A fruit is a mature (ripened) ovary that contains one or more seeds.
A seed is a mature ovule consisting of the following parts:
Seed coat (for protection)
Embryo (immature plant)
Endosperm (for food)
An embryo can consist of the following parts:
One cotyledon (monocot plants)
Two cotyledons (dicot plants)
Epicotyl that forms leaves
Hypocotyl that forms stem and root
Seeds can germinate (sprout) under favorable conditions, the most important of which are warmth and moisture.

56. Quiz: Fill In The Blanks…
After an ovule is fertilized, it develops into a seed. The ovary, meanwhile, becomes the ____________. The ____________ within a seed consists of an epicotyl, a hypocotyl and one or more cotyledons. Monocot seeds, such as corn, have one cotyledon, and _____________ seeds, such as beans, have two cotyledons. The two most important factors that affect seed germination are moisture and ____________.
fruit
embryo
dicot
warmth

57. Testing Your Knowledge
Section Five
Testing Your Knowledge

58. This Is A Test of What You Have Learned…
There are 10 questions on this test.
Try to correctly answer all of the questions.
If you miss a question, watch the screen for an explanation of the correct answer.

59. Select The Best Matching Choice:
Cotyledon:
Answer Column:
Immature seed
Spread far and wide
Sprout stem and roots
Immature fruit
Diploid cell
Male plant gamete
Plant embryo part
True plant leaf
Correct Answer: G
The cotyledon is the part of a plant embryo that often provides food during germination. Monocot plant embryos have one cotyledon, and dicot plant embryos have two cotyledons.
Germinate:
Correct Answer: C
When a seed germinates, it sprouts roots and a stem. Germination occurs under various conditions that depend on the type of seed.

60. Select The Best Matching Choice:
Pollen:
Answer Column:
Immature seed
Spread far and wide
Sprout stem and roots
Immature fruit
Diploid cell
Male plant gamete
Plant embryo part
True plant leaf
Correct Answer: F
Pollen is the male gamete of plants produced in the anthers of plants that have stamens. Female plants that lack stamens cannot produce pollen.
Ovule:
Correct Answer: A
An ovule is the immature seed of a plant that develops from the embryo sac within the ovary.

61. Select The Best Choice To Complete Each Analogy:
seed
A fruit is to a flower ovary as a(n) ________ is to an ovule.
A. sepal
B. seed
C. calyx
D. gamete
E. pistil
Since a fruit is a ripened flower ovary, it is most like a seed, which is a ripened flower ovule.

62. Select The Best Choice To Complete Each Analogy:
ovary
An anther is to a stamen as a(n) ______________ is to a pistil.
A. ovule
B. style
C. filament
D. ovary
E. petal
Since the anther is the gamete producing structure of a stamen, it is most like the ovary, which is the gamete producing structure of a pistil.

63. Fill In The Blanks… flowers fertilization fruit germinate
Many higher plants are equipped with specialized reproductive structures, called ______________, which allow them to reproduce sexually. During the process of ______________, male and female gametes combine to form a zygote. The ovary matures into a structure called a(n) ______________, and the ovules within it mature into seeds. Seeds are dispersed by several means and can ______________ (begin to grow) to form new plants.
flowers
fertilization
fruit
germinate

64. Pollination & Fertilization
Biology Basics
Review!
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Pollination & Fertilization
~Seeds, Fruits and Embryos~