BOT 101 ALE #6 Sexual Life Cycles of Plants

Name______

BOT 101 ALE #6 Sexual life cycles of plants

1. What is happening in the cell during each phase of the cell cycle? Interphase: G1 Growth

S DNA Replication

G2 Growth, preparation for cell division

M phase: Mitosis – division of the nucleus Cytokinesis – division of the cytoplasm to form 2 cells

2. Draw a series of cells depicting the stages of mitosis. Label the stages.

Compare your drawings to the drawings of mitosis in your text book or lecture notes

3. What are sister chromatids? How do sister chromatids compare genetically?

Sister chromatids are two molecules of DNA held together at the centromere of one chromosome. They are genetically identical because one sister chromatid is formed from the replication of the other chromatid.

4. What are homologous chromosomes?

chromosomes of same size & shape but different genetic origins (one from the “mom plant,, one from “dad”). Each member of a homologous pair has the same order and location of genes. However, the two chromosomes are not identical because they can have slightly different versions of the same gene.

Meiosis 5. a. What is the function of meiosis? to produce gametes, cells with half the number of chromosomes as their parent cells. Gametes function in sexual reproduction b. What kinds of cells are produced by meiosis?_____sex cells (gametes)

c. Are these cells haploid or diploid? ______haploid______

6. Overview of Meiosis…

1 a. How do the chromosomes align at metaphase I of meiosis? With their homologous pairs b. What separates during anaphase I of meiosis? Homologous pairs c. How do the chromosomes align at metaphase II of meiosis? Individually, randomly d. What separates during anaphase II of meiosis? Sister chromatids e. Are the daughter cells haploid or diploid? Haploid

7. Compare mitosis and meiosis by completing the table below.

Mitosis Meiosis All cells of the plant Only the cell of the Type of cells involved except those in the sporangium undergo sporangium meiosis, to create spores 1 2 Number of cell divisions involved

2 4 Number of daughter cells

same different How do the daughter cells compare genetically?

diploid haploid Are the daughter cells diploid (2n) or haploid (n)?

no yes Involves homologue pairing and cross over?

2 8. Draw and label the generalized diagram of the alternation of generations. Be sure to label mitosis and meiosis, and indicate which parts of the cycle are haploid and which are diploid

Item: Cells: #chrom. How form: What is reproductive job? single sets: mitosis? or multi? haploid or meiosis? fert? diploid? spore Single Haploid Meiosis Divides by mitosis to make the gametophyte gametophyte Multi Haploid Mitosis Divides by mitosis to make gametes gamete Single Haploid Mitosis Are egg and sperm – cells fuse to form the diploid zygote zygote Single Diploid Fertilization Divides by mitosis to create the sporophyte sporophyte multi diploid mitosis Has a region called the sporangium which divides by meiosis to make spores

3 The moss lifecycle Step 1. A tiny spore blows in the wind, lands in moist soil, and sprouts into a leafy plant. Step 2. At the top of the moss plant, hiding within its leaves, eggs form within little cups. Neighboring moss plants make sperm inside little sacs. Step 3. The eggs give off chemicals to beckon the sperm who swim within a film of rain water. Step 4. The fertilized egg (zygote) sprouts into a tall stalk, up into the air currents. At the tip of the stalk is a capsule where spores are made via meiosis and released into the wind.

B. Moss questions based upon the story above: 1. Does “sprouting” happen via mitosis? yes 2. Are moss gametes (eggs and sperm) made via meiosis as they are in animals? No, they are made by mitosis 3. The spores are made via meiosis... so are the spores haploid or diploid? haploid 4. The leafy plants are made from a sprouted spore... so are the leaves haploid or diploid? haploid 5. How is spore different from a gamete? Spores are made by meiosis, gametes are made by mitosis. Both spores and gametes and single-celled and haploid, by spores can grow by mitosis into a mutlicellular structure (the gametophyte) without fusing to any other cell. Gametes must fuse together before they can divide by mitosis to make the sporophyte.

6. How does moss get up onto your roof? Mosses release their spores into the wind, which travel up to your roof

FERNS ....will represent the SEEDLESS VASCULAR PLANTS Their story sounds a lot like the moss story... with a few subtle twists.

A. The Fern lifecycle Step 1. A tiny fern spore blows in the wind, lands in moist soil, and sprouts into a little heart-shaped flat thing. Step 2. The heart-shaped thing makes egg cups and sperm sacs on its surface.

4 Step 3. The eggs give off chemicals to beckon the sperm who swim within a film of rain water (from one “heart” to another). Step 4. The fertilized egg (zygote) sprouts into a leafy fern plant. On the surface of the leaves, many spore capsules form. Spores are made via meiosis and tossed into the wind.

B. Questions based upon the life cycle story

1. Is the flat heart-shaped thing diploid or haploid? haploid 2. Are the fern leaves haploid or diploid? diploid 4. Where would you find fern zygotes? Within the archegonia, which is a part of the fern gametophyte ( the tiny heart-shaped thing 5. What is the “job” of a fern spore? To disperse on the wind or water, finding a suitable place to begin growing by mitosis into a new fern gametophyte. 6. What is the technical name for the heart-shaped thing? The gametophyte 7. What is the technical name for the stage when ferns have roots, stems, leaves and spore capsules? The sporophyte 8. What is the technical name for spore capsules? Sporangium

PINES will represent the Gymnosperms

The general steps are the same in pines as they are in moss and ferns but many of the stages are very small and happen inside cones. The scales of the cones are modified leaves. On the surface of each leaf are sporangia.

A. The Pine Lifecycle Step 1. Spores are made via meiosis within tiny male cones and tiny female cones. The spores do not go anywhere. Step 2. : In the male cones, the spores divide a few times then get coated with a hard material. They have become pollen grains. They are sperm in a capsule! They are the male gametophytes. They blow in the wind and the

5 male cones shrivel up and fall off. In the female cones’ sporangia, all the spores die except one. That remaining spore divides many times, making an egg or two within sacs, surrounded by nutritious tissue. Step 3. The pollen lands on the female cones (usually before they are even done making the eggs) and starts growing a tube towards the eggs. The sperm nucleus slides down the tube and fertilizes the egg. Step 4. The fertilized egg (zygote) divides to form an embryo surrounded by nutritious female gametophyte tissue. The sporangium sac hardens into a seed coat. The seed falls out and grows into a new tree.

B. Questions based upon the life cycle story

1. Why is it adaptive for the sperm to be wrapped in a hard coat and travel in the air? It’s wrapped in a hard coat c to protect it from dessication (drying out). It travels in the air so that the sperm can travel far enough to reach the female cones of another tree. This means that the trees don’t have to rely on water for fertilization. The sperm of these trees don’t have flagellated sperm, like mosses and ferns do.

2. Why is it adaptive for the embryo to be wrapped inside a seed? When the seed it below the ground, it is covered by soil and so there is not enough sunlight for photosynthesis. The tissues of the seed will nourish the germinating plant until it has leaves that can photosynthesize. The tissues of the seed also prevent the embryo from drying out.

FLOWERING PLANTS

Flower Lifecycle- : Fill in the blanks

Step 1. A plant has matured and formed a young flower. Step 2. Within the sporangia sacs of the anthers, spores are made via meiosis___. The spores each divide a few times to form pollen grains (the male gametophytes). Step 3. Meanwhile, in the ovules, spores are made via meiosis and only one survives. The survivor divides three times to make 8 nuclei in communal cell. One of these is the egg. These 8 nuclei are the female gametophyte______.

6 Step 4. Pollination: Pollen lands on the female’s stigma and grows a pollen____ tube___. Step 5. Fertilization: the tube reaches the egg, and one sperm cell slides down the tube and unites with the egg. Then a second sperm slides down and unites with TWO other female nuclei to make a triploid (3n) cell in a unique process called “double fertilization______”. Step 6. The embryo grows. The triploid tissue grows also and is future food for the baby. It is called “endosperm” and is a milky white fluid. The ovule wall becomes a seed coat. The ovary (and sometimes other parts like the receptacle) will mature to become the f ruit ____.

9. Compare and contrast Monocots & Dicots. What characteristics would you use to identify a plant as one or the other? Monocots are defined as having one seed leaf; Dicots have two seed leaves. This characteristic is impossible to know without dissecting the seed. In order to decide whether the plant is a monocot or dicot, it may be easier to look at other characteristics. Monocots typically have parallel leaf veins and flower parts in threes. Dicots typically have netlike leaf veins and flower parts in fours or fives.

10. Describe the move of plants onto land. What challenges did plants need to overcome in order to successfully live & reproduce on land? What adaptations allowed them to overcome these challenges? Plants evolved from freshwater and marine algae that obtained mutations that allowed them to live successfully on land. On land, these ancient plants needed to obtain water (to avoid dessication), protect themselves against UV radiation, and resist new pathogens and herbivores (much later in time). Plant acquired mutations that allowed them to successfully photosynthesize (obtain food) and reproduce under these new environmental conditions. The 5 adaptations that all members of Kingdom Plantae share include apical meristems, alternation of generations, walled spores produced in sporangia, multicellular gametangia, and multicellular, dependent embryos. Additional adaptations that some (most) members of Kingdom Plantae acquired include, cuticles, roots, shoots, secondary compounds, stomata, lignin in cell walls, vascular system.