1. Plants
Chapters 21-23

2. Evolution of Plants Adapting to Land
Nothing lived on land until an ozone layer formed – the ozone layer offered protection from the sun’s intense UV radiation. With life on land came adaptations for survival:
Preventing water loss
Reproducing by spores & seeds
Abilities to transport materials
throughout the plant

3. Preventing Water Loss
Cuticle – a waxy protective covering that prevents water loss
The cuticle kept water in, but kept O2 and CO2 out.
Plants developed a stomata (little mouth) – a small opening in the leaf that allows for gas exchange.

4. Reproduction
Reproduction by spores and seeds helps protect reproductive cells from drying out.
spore – haploid (n) reproductive cell surrounded by a hard outer wall
Seed – embryo, diploid (2n) surrounded by a protective coat
endosperm – tissue that provides nourishment for the developing embryo

5. Transporting materials throughout the plant
Vascular tissue – transports water and dissolved substances from one part of the plant to another
Xylem – carries water and inorganic nutrients from the roots to the stems and leaves
Phloem – carries organic compounds and some inorganic nutrients in any direction

6. Some plants developed woody tissue and grew to great heights
This gave them an advantage in gathering light.
Woody tissue
Several layers of xylem
Usually brown, woody stems
Non-woody plants
Herbaceous
Soft, green stems

7. Classifying Plants

9. A Cladogram of Plant Groups
Flowering plants
Cone-bearing plants
Ferns and their relatives
Mosses and their relatives
Green algae ancestor
Flowers; Seeds Enclosed in Fruit
Seeds
Water-Conducting (Vascular) Tissue
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10. Bryophytes, Seedless Plants, Gymnosperms & Angiosperms
When we classify plants, what question do we first ask?
Vascular or non-vascular?
Let’s look at non-vascular first
Bryophytes do not have vascular tissue

11. Bryophytes – Non-Vascular
Bryophytes include:
Mosses (most common)
Liverworts
Hornworts
Help! I Need Water!!!
Bryophytes have life cycles that depend on water for reproduction
Since they don’t have vascular tissue, the plants draw up water by osmosis.

12. Dependence on water keeps bryophytes small in size
Bryophytes are low-growing plants found in moist, shaded areas.
Lack of vascular tissue means that bryophytes do not have true roots.
Bryophytes have rhizoids – long, thin cells that anchor them to the ground and absorb water and minerals from the soil (by osmosis).

13. The gametophyte stage of moss
Hornworts
Liverworts

14. Reproduction
For fertilization to occur, the sperm must swim to an egg.
Because of this limiting factor, bryophytes must live near water.
Remember, bryophytes need water to reproduce !!!

15. Vascular Plants Vascular plants have vascular tissue
Xylem – carries water upward from the roots to every part of the plant
Phloem – transports solutions of nutrients and carbohydrates produce by photosynthesis (all directions)
Produce lignin – makes cell walls rigid.
Allows vascular plants to grow upright and reach great heights

16. Vascular plants have true roots, leaves and stems
Roots – underground organs that anchor plants, and absorb water and minerals
Leaves – photosynthetic organs – one or more bundles of vascular tissue gathered into veins made of xylem and phloem

17. Stems – supporting structures that connect roots and leaves, carrying water and nutrients between them.
Vascular plants have a life cycle in which the sporophyte is the dominant stage.
Remember, first we ask vascular or non-vascular?
Next, we ask seeds or seedless?

18. Seedless vascular plants
Include:
Whisk ferns
Club mosses
Horsetails
Ferns (most common)
Seedless vascular plants have true vascular tissue, strong roots, rhizomes (underground stems), fronds (large leaves)

19. The whisk fern are rare. They are usually found in tropical and subtropical regions.

20. The club moss is sometimes known as a ground pine.

21. Horsetails
Tree ferns

22. Seed Plants We have asked vascular or not-vascular?
We then asked seeds or seedless?
Seed plants can be further classified:
Gymnosperms (unprotected seeds on cones)
Includes conifers, cycads, ginkoes, gnetophytes
Angiosperms (flowering plants with protected seeds)
Includes grasses, flowering trees and shrubs, wildflowers and cultivated flowers

23. Reproduction free from water
Adaptations that allow reproduction without water
Flowers or cones
Transfer of sperm by pollination
Protection of embryos in seeds
A seed coat surrounds the embryo. It also contains a stored food supply for the embryo.

24. Angiosperms can be further classified:
Named for the number of seed leaves (cotyledons) in the plant embryo
Monocots have one seed leaf
Dicots have two seed leaves

25. Comparison of Monocots and Dicots
Single cotyledon
Parallel veins
Floral parts often in multiples of 3
Vascular bundles scattered throughout stem
Fibrous roots
Two cotyledons
Branched veins
Floral parts often in multiples of 4 or 5
Vascular bundles arranged in a ring
Taproot
Seeds
Leaves
Flowers
Stems
Roots
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26. Roots, Stems and Leaves
The three principle organs of seed plants are:
Roots
Stems
Leaves

27. Roots Two main types of roots Taproots – found mainly in dicots
Fibrous roots – found mainly in monocots
Two functions of roots
Anchor a plant in the ground
Absorb water and dissolved nutrients from the soil

28. Stems Three functions of stems: Produce leaves, branches and flowers
Hold leaves up in the sunlight
Transport substances between roots and leaves
The vascular tissue of stems lifts water from the roots to the leaves (xylem) and sends the products of photosynthesis from the leaves to other parts of the plant (phloem)

29. Leaves Main function is photosynthesis
The broad, flat surface of leaves helps increase the amount of sunlight absorbed by plants
Other functions of leaves:
Transpiration
Gas exchange

30. Connects with exterior through stomata – allows CO2 and O2 to diffuse in and out of the leaf
Each stoma consists of two guard cells that control the opening and closing of the stomata by responding to changes in water pressure.

31. Transpiration
Transpiration is the loss of water from a plant through its leaves.
The water is replaced by water drawn into the leaf through the xylem vessels in the vascular tissue.

32. A B Evaporation of water molecules out of leaves.
Pull of water molecules upward from the roots.

33. Gas Exchange
Plants keep their stomata open just enough to allow photosynthesis to take place, but not so much that they lose an excessive amount of water.
Guard cells control the stomata through changes in water pressure.
when water pressure in guard cells is high, stoma is open
When water pressure in guard cells is low, stoma is closed.

34. In general, stomata open in the daytime, when photosynthesis is active, and close at night to prevent water loss.
A plant will close its stomata any time water conservation is an issue.

35. Reproduction of Seed Plants
Reproduction in gymnosperms takes place in cones.
Pollen cones – male cone – produce pollen grains (male gametophytes)
Seed cones – female cone – produce female gametophytes
Gymnosperm pollen is carried by the wind to female cones (pollination)

36. Angiosperms
Flowers are reproductive organs composed of four kinds of specialized leaves:
Sepals
Petals
Stamen
Carpels

37. Sepals – resemble leaves
Sepals – resemble leaves. Enclose the bud before it opens; protect the flower while it is developing.
Petals – often brightly colored (the pretty part). It attracts insects and other pollinators.
Stamen (boy parts)
anther – produce male gametophytes (pollen)
filament – supports anther

38. Carpel (girl parts) sometimes called pistils
ovary – produces female gametophytes
style – stalk
stigma – sticky portion where pollen lands

39. The Structure of a Flower
Filament
Anther
Stigma
Style
Ovary
Carpel
Petal
Sepal
Ovule
Stamen

40. Pollination Most gymnosperms and some angiosperms are wind pollinated
Most angiosperms are pollinated by animals (beneficial to both plant and animal)
For fertilization to occur, pollen grains land (or are carried) on the stigma of an appropriate flower.
Pollen (male gametes) reach the ovary (where female gametes are made) and fertilization occurs

41. Seed Development & Germination
Once fertilization occurs, nutrients flow into the flower tissue to support the growing embryo within the seed.
As seeds mature, ovary walls thicken to form a fruit that encloses developing seeds
A fruit is a ripened ovary that contains angiosperm seeds.
The term “fruit” applies to any seed (even vegetables) enclosed within its embryo wall

42. Why do angiosperms produce fruit? Two ways seeds can be dispersed
To disperse seeds
Two ways seeds can be dispersed
animals
Typically contained in fleshy, nutritious fruits
wind and water
Typically lightweight
Allows them to be carried in the air or float on the surface of the water

43. Some plants develop right away, others “wait”
Environmental factors like temperature and moisture determine when a seed develops
dormancy – embryo is alive but not growing
germination – early growth stage of the plant embryo

44. Seed Germination Seed absorbs water
Absorbed water causes the endosperm to swell, cracking open the seed coat
Through the cracked seed coat, the young root emerges and begins to grow

45. Three categories of plant life spans
annuals – flowering plants that complete a life cycle within one growing season
biennials – complete their life cycle in two years
perennials – flowering plants that live for more than two years

46. Concept Map Plants are categorized as Annuals Biennials Perennials
that complete their life cycle in
that complete their life cycle in
that complete their life cycle in
1 growing season
2 years
More than 2 years
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47. Plant Responses
The response of plants to environmental stimuli are called tropisms.
Tropisms demonstrate the ability of plants to respond effectively to conditions in which they live

48. Light & Gravity
The response of a plant to light is known as phototropism
Phototropism causes a plant to grow toward a light source
The response of a plant to gravity is known as gravitropism

49. Gravitropism
Gravitropism causes the shoots of a germinating seed to grow out of the soil - against the force of gravity
It also causes the roots of a plant to grow with the force of gravity and into the soil

50. Response to Touch
The response of plants to touch is called thigmotropism.
An example of thigmotropism is the growth of vines and climbing plants.

51. Any Questions ???