1. Plant Growth, Reproduction, and Response
Unit 10

2. Plant Life Cycles

3. Plant Life Cycle
Plant life cycles alternate between producing spores and gametes.
The plant life cycle in which the plant alternates between haploid (1n) and diploid (2n) phases is called alternation of generations.

4. Plant Life Cycle
The diploid phase of a plant life cycle begins with a fertilized egg, called a zygote. A zygote divides by mitosis and grows into a mature sporophyte, or spore-producing plant.
A spore makes the beginning of the haploid phase of the plant life cycle. A spore divides by mitosis and grows into a mature gametophyte, or gamete-producing plant.

5. Plant Life Cycle

6. Plant Life Cycle

7. Plant Life Cycle
NOTE: Mitosis can occur in haploid cells as well as diploid ones.
A haploid set of chromosomes, and hence a single set of genes, is sufficient to control cell function in these organisms (but not in most animals).
The gametophyte generation is the major stage in the life of mosses and an independent plant in ferns.

8. Life Cycle of Nonvascular Plants: Moss
gametophyte phase is dominant
sporophytes are stalk-like structures that grow up from the gametophyte
capsule at tip of moss sporophyte contains spore-producing sacs called sporangia
when mature, capsule opens  spores released

9. Life Cycle of Nonvascular Plants: Moss
moss gametophyte produces gametes
male: sperm (many)
female: egg (1)
sperm swim toward egg if water is present  fertilization
after fertilization, sporophyte phase begins once again

10. Life Cycle of Nonvascular Plants: Moss

11. Life Cycle of Seedless Vascular Plants: Ferns
sporophyte is dominant phase (for all vascular plants)
underside of a fern leaf (frond)  sori
clusters of sporangia (spore-producing sacs)
spores released when mature
can develop into a gametophyte if conditions are favorable for growing

12. Life Cycle of Seedless Vascular Plants: Ferns
prothallus: fern gametophyte (about the size of your little fingernail
anchors to soil with tiny threadlike structures called rhizoids
contains special reproductive structures that produce sperm and eggs

13. Life Cycle of Seedless Vascular Plants: Ferns
If freestanding water is present,
male structures release sperm
sperm swim  egg  fertilization
zygote forms on the prothallus
beginning of sporophyte generation
Zygote grows above prothallus  mature sporophyte
fiddleheads: newly forming fronds

14. Life Cycle of Seedless Vascular Plants: Ferns

15. Life Cycle of Seed Plants: Conifers
sporophyte: familiar form (for all seed plants)
seed plants produce two types of spores that develop  male and female gametophytes
gametophytes of seed plants are microscopic

16. Life Cycle of Seed Plants: Conifers
Example: pine tree
branches have two different types of cones (male & female)
female cones  larger and more scaly; live and grow for several years
each scale of a female pinecone: 2 ovules that produce spores
1 spore/ovule  gametophyte
male cones live only for a few weeks
male spores  pollen grains (male gametophyte)

17. Life Cycle of Seed Plants: Conifers
male cones release clouds of pollen in the spring
pollen grain lands on a female cone, sticks
pollination: pollen grain reaches opening of ovule.
eggs are produced inside the ovule
pollen tube begins to grow from pollen grain  egg
In pine species, it takes a year for pollen tube to reach egg

18. Life Cycle of Seed Plants: Conifers
2 sperm develop inside pollen grain travel down pollen tube toward egg
no flagella (don’t need to swim through water to reach egg)
1 sperm may fertilize an egg  zygote  embryo
ovule  protective pine seed
each scale: 2 developing pine seeds
when seeds mature, scales open up and release them
life cycle starts over w/new sporophyte (pine tree seedling)

19. Life Cycle of Seed Plants: Conifers

20. Take Home Message
All plants alternate between two phases in their life cycles.
Plant life cycles alternate between producing spores and gametes.
Life cycle phases look different among various plant groups.

21. Reproduction in Flowering Plants

22. Reproduction in Flowering Plants
Flowers contain reproductive organs protected by specialized leaves.
The outermost layer of a flower is made up of sepals – modified leaves that protect the developing flower.
The layer inside the sepals is made up of petals, which are modified leaves.
protect reproductive structures
attract pollinators

23. Reproduction in Flowering Plants

24. Reproduction in Flowering Plants
Some species have flowers with only male or only female structures, but the flowers of most species have BOTH.

25. Reproduction in Flowering Plants
male part of a flower: stamen
filament supports anther, which produces pollen grains (male gametophytes)
female (inner) part of a flower: carpel
several carpals fused together form pistil
female gametophytes are produced inside the ovary (at base of flower)

26. Reproduction in Flowering Plants

27. Reproduction in Flowering Plants
Pollination  wind or animals (more reliable)
Insects, birds, and animals that visit flowers collect pollen as a food source.
When the animal searches for food in another flower, pollen from the first flower brushes against the stigma of another flower.

28. Reproduction in Flowering Plants

29. Reproduction in Flowering Plants

30. Reproduction in Flowering Plants
Fertilization takes place within the flower.
Anthers produce pollen grains (male gametophyte)
Cells w/in anthers divide by meiosis  4 spores
Spores divide by mitosis  2 haploid cells
Along with protective these 2 cells form a pollen grain

31. Reproduction in Flowering Plants
Fertilization takes place within the flower.
One cell in ovule divides by meiosis to form 4 spores (3 usually die)
Remaining spore divides 3 times to form embryo sac (female gametophyte)
One large, central cell has 2 haploid polar nuclei
One of the other cells develops  egg

32. Reproduction in Flowering Plants
Double Fertilization
After pollination, one cell in pollen grain grows into a pollen tube
Extends down style  ovule
Other cell in pollen grain divides by mitosis  2 sperm
Both travel down pollen tube
One sperm fertilizes egg
Other sperm combines w/polar nuclei in embryo sac

33. Reproduction in Flowering Plants
Double Fertilization
The sperm cell that does NOT fertilize the egg has a triploid (3n) nucleus and becomes the endosperm, a food supply for the developing plant embryo.
Only happens in flowering plants!

34. Reproduction in Flowering Plants

35. Reproduction in Flowering Plants – Animation
Double Fertilization

36. Flowering Plants Life Cycle
A tomato plant is a typical flowering plant. If the flower is pollinated and fertilization occurs, ovules will develop into seeds and the surrounding ovary will develop into a fruit.

37. Flowering Plants Life Cycle

38. Flowering Plants Life Cycle

39. Flowering Plants Life Cycle

40. Flowering Plants Life Cycle

41. Seeds and Fruit At fertilization, ovule becomes a seed embryo
nutritious endosperm
protective seed coat

42. Seeds and Fruit
Using nutrients provided by endosperm, embryo develops 1-2 cotyledons, which sometimes provide nourishment for the new plant before it can begin producing its own food through photosynthesis

43. Seeds and Fruit
While the seed develops, the surrounding ovary grows into a fruit.
Flowering plants that produce many seeds w/in 1 ovary – larger fruit

44. Seeds and Fruit
After a pumpkin flower (left) is pollinated and fertilization occurs, seeds and fruit begin to develop. The pumpkin fruit (center) is green at first, containing immature seeds. The ripe fruit (right) is orange and contains
mature pumpkin seeds.

45. Seed Dispersal and Germination
Animals, wind, and water can spread seeds.
Recall that when a seed develops, the surrounding ovary grows into a fruit.
Animals eat the fruit, and use their ‘waste’ as fertilizer (with the undigested seed inside), to make new seed plants.

46. Seed Dispersal and Germination

47. Seed Dispersal and Germination
Seeds begin to grown when environmental conditions are favorable.
When a seed is dormant, or under dormancy, the embryo stops growing.
This happens if the temperature, moisture, oxygen, and/or light levels are not favorable to the seed.

48. Seed Dispersal and Germination
Many types of seeds begin to grow when there are certain changes in temperature, moisture, or light levels.
During germination, the embryo breaks out of the seed coat and begins to grow into a seedling.
Embryo takes up water
Water causes the seed to swell and crack
Embryonic root breaks through the crack as it grows
Young plant is free of seed coats and grows!

50. Asexual Reproduction
Plants can that can grow a new individual from a fragment of a stem, leaf, or root are reproducing by regeneration.
Most plants have a way of cloning themselves through asexual reproduction.

51. Asexual Reproduction
Humans can produce plants with desirable traits using vegetative structures.
Example: seedless fruit

52. Plant Hormones and Responses
Plant hormones regulate plant functions.
A hormone is a chemical messenger produced in one part of an organism that stimulates or suppresses the activity of cells in another part.
In humans, hormones control functions vital to survival and reproduction.
In plants, when a hormone meets the right receptor, it triggers a response.

53. Plant Hormones and Responses

54. Plant Hormones and Responses
Types of plant hormones and their functions:
Gibberellins – produce increase in size in plants
Ethylene – causes ripening in fruits
Cytokinins – stimulate cytokinesis, the final stage of cell division
Auxins – lengthening of plant cells

55. Plant Hormones and Responses
Phototrophism – tendency of plant to grow towards light (light)
Thigmotrophism – plants response to touch (touch)
Gravitrophism – up-and-down growth of plant due to Earth’s gravitational pull (gravity)
Photoperiodism – plants response to changing of days and night throughout the year (season changes)

56. Plant Hormones and Responses

57. Take Home Message
Reproduction of flowering plants takes place within flowers.
Flowers contain reproductive organs protected by specialized leaves.
Flowering plants can be pollinated by wind or animals.
Fertilization takes place within the flower.