1. Reproduction in Plants

2. Alternation of Generation
Plant life cycles undergo alternation of generation of two multicellular stages
This involves alternating between diploid (2N) and haploid (1N) generation
The sporophyte is diploid, and in all angiosperms, the roots, stems, leaves and flowers are part of the sporophyte generation

3. Flower Structure Flowers
Are composed of four floral organs: sepals, petals, stamens, and carpels, which are modified leaves

4. Sepals - green leaflike parts that protect developing flower

5. Stamen is the male reproductive organ
The anther located at the tip of the stamen, is where meiosis occurs to produce pollen grains
Pollen grains contain sperm
Carpel (pistil) is the female reproductive organ
The ovary located at the base of the carpel contains ovules

6. Flowers that lack one or more of the four parts are incomplete flowers
Flowers that contain both stamens and carpels are said to be perfect, those with only stamens or carpels are imperfect

7. Staminate flowers have only stamens (imperfect)
Carpellate flowers contain only carpels (imperfect)
Flowers that are imperfect, and contain both male (staminate) and female (carpellate) flowers on the same plant are monoecious

8. Many variations in floral structure
Have evolved during the 140 million years of angiosperm history

9. Pollination
Pollination is the transfer of pollen from an anther to the stigma of a carpel
Self-pollination occurs if the pollen is from the same plant
Pollination can occur by wind, water, insects, birds, bats, and other mammals

10. Pollination enables gametes to come together within a flower
In angiosperms, the dominant sporophyte
Produces microspores that develop within flowers into male gametophytes (pollen grains)

11. Pollen
Develops from microspores within the sporangia of anthers

12. Embryo sacs
Develop from megaspores within ovules

13. Double Fertilization
The ovule contains the embryo sac which is the female gametophyte
Pollination must precede fertilization,most angiosperms depend on animals for fertilization
The tube cell gives rise to the pollen tube, and the generative cell divides to form two sperm
One sperm fertilizes the egg to become the zygote, and the other fertilizes the large diploid cell to become the triploid (3N) endosperm which nourishes the embryo

14. Gametophyte Development and Pollination
In angiosperms
If pollination is successful, a pollen grain produces a structure called a pollen tube, which grows down into the ovary and discharges sperm near the embryo sac

15. Growth of the pollen tube and double fertilization

16. After double fertilization
From Ovule to Seed
After double fertilization
The ovary develops into a fruit enclosing the seed(s)

17. Endosperm Development
Usually precedes embryo development
In most monocots and some dicots
The endosperm stores nutrients that can be used by the seedling after germination
In other dicots

18. Structure of the Mature Seed
The embryo and its food supply

19. In a common garden bean, a dicot

20. The seeds of other dicots, such as castor beans
Have similar structures, but thin cotyledons

21. The embryo of a monocot
Has a single cotyledon, a coleoptile, and a coleorhiza

22. From Ovary to Fruit A fruit Develops from the ovary
Protects the enclosed seeds

23. Fruit Types and Seed Dispersal
Simple Fruits
Simple fruits are derived from single or several united carpels
Legumes are fruits that split along two sides when mature
Dehiscent - Split open

24. Simple Fruits Fleshy Dry Drupe Berry Pome Follicle Legume Capsule
Achene
Nut
Grain

25. Simple Fruits Dispersal Many seeds are dispersed by wind
Woolly hairs, plumes, wings
Fleshy fruits - Attract animals and provide them with food
Peaches, cherries, tomatoes
Accessory fruit - Bulk of fruit is not from ovary, but from receptacle

26. Compound fruits develop from several individual ovaries
Aggregate Fruits
Ovaries are from a single flower
Blackberry
Multiple Fruits

27. Fruits are classified into several types
Depending on their developmental origin

28. Seed Germination As a seed matures
It dehydrates and enters a phase referred to as dormancy

29. Environmental requirements for seed germination
Availability of oxygen for metabolic needs
Adequate temperature for enzyme activity
Adequate moisture for hydration of cells
Light (in some cases)

30. Length of time seeds retain their viability is quite variable
Seed Germination
Length of time seeds retain their viability is quite variable
Some seeds do not germinate until they have been through a dormant period
Temperate zones - Cold Weather
Deserts - Rain

31. Seed Germination
In some seeds, the seed coat (testa) must be disrupted or scarified before water uptake
Often must pass through digestive tract of animals

32. Seed Dormancy: Adaptation for Tough Times
Increases the chances that germination will occur at a time and place most advantageous to the seedling
The breaking of seed dormancy

33. Seed metabolism during germination
Uptake of water
Gibberellin released after water uptake
Amylase results in the hydrolysis of starch (stored in endosperm or cotyledons) into maltose
Maltose broken down into glucose which can be used in cellular respiration or to build cellulose for cell walls

34. From Seed to Seedling
Germination of seeds depends on the physical process called imbibition, the uptake of water due to low water potential of the dry seed
The hydrated seed expands, ruptures the seed coat, and triggers metabolic changes that make the embryo start to grow

35. The radicle In many dicots
Is the first organ to emerge from the germinating seed
In many dicots
A hook forms in the hypocotyl, and growth pushes the hook above ground

36. Monocots The coleoptile
Use a different method for breaking ground when they germinate
The coleoptile

37. Phytochromes as Photoreceptors

38. A phytochrome is the photoreceptor responsible for the opposing effects of red and far-red light

39. The pigment phytochrome responds to the presence or absence of light by changing forms between Pred (Pr) and Pfar red (Pfr)
Pr is changed by exposure to red light to become Pfr
Pfr is changed back to Pr by exposure to far-red light, conversion in darkness, or enzymatic degradation
The leaves produce a hormone that induces flowering in response to levels of Pfr

40. Phytochromes exist in two photoreversible states
With conversion of Pr to Pfr triggering many developmental responses

41. Biological Clocks and Circadian Rhythms
Many plant processes
Oscillate during the day

42. Many legumes lower their leaves in the evening and raise them in the morning

43. Many plants open their flowers during the day, and close them at night

44. Cyclical responses to environmental stimuli are called circadian rhythms and are approximately 24 hours long
Circadian rhythms occur with or without external stimuli such as sunrise and sunset
The light-dark cycle of day and night provide cues that fine tune biological clocks and keep them precisely synchronized to a period of exactly 24 hours
This biological clock is located in a cluster of nerve cells located in the hypothalamus of the brain in humans and mammals

45. Researchers have identified genes that control biological clocks in rodents, fruit flies, bacteria, and some plants
These genes encode a transcription factor that builds up over time
At high concentrations, the same gene is turned off
When concentrations fall, transcription begins again

46. The Effect of Light on the Biological Clock
Phytochrome conversion marks sunrise and sunset

47. Photoperiodism and Responses to Seasons
Photoperiod, the relative lengths of night and day
Is the environmental stimulus plants use most often to detect the time of year
Photoperiodism

48. Photoperiodism and Control of Flowering
Some developmental processes, including flowering in many species

49. Short day plants flower when day length is below a critical value, or more correctly, short day plants flower when the length of night exceeds the minimum critical night length
Short day plants are really long night plants
Long day plants bloom when day length exceeds the critical value, or when the length of night does not exceed the maximum critical night length
Long day plants are short night plants

50. Critical Night Length
In the 1940s, researchers discovered that flowering and other responses to photoperiod
Are actually controlled by night length, not day length

51. Phytochrome is the pigment that receives red light, which can interrupt the nighttime portion of the photoperiod

52. Short bursts of red or white light can cause the critical night length (length of continuous darkness) to be interrupted
A flash of far-red light reverses this effect and does not interrupt length of continuous darkness

53. A Flowering Hormone?
The flowering signal, not yet chemically identified