Ch 24 Reproduction in Plants

24.1. Life Cycles of Mosses, Ferns and Conifers

A. Alternations of Generations – all plants alternate between ______(n) and ______(2n) stages.

1. Asexual reproduction occurs when the new plant has the same genetic make-up as the original

a. ______- a new plant is produced from an existing vegetative structure

B. Life cycle of Mosses – gametophyte stage is dominant

1. ______– produced by a spore, it is a small green filament of cells that develops into either a male or female gametophyte

C. Life Cycle of Ferns – ______stage is dominant. Ferns produce spores in sori on the back of the leaves. A spore germinates into a heart-shaped gametophyte called a prothallus which can produce both archegonia and antheridia.

D. Life Cycle of Conifers - sporophyte stage is dominant. Adult conifers produce male (pollen) and female (ovule) cones on separate branches. Pollination occurs when pollen fall near the opening of a female cone. Seeds are released when the cone opens. If conditions are right, the seed will germinate.

a. ______– a female spore that eventually becomes the female gametophyte (which holds 2+ eggs) / b. ______– develops into a male gametophyte (pollen grain) / c. ______– ovule opening through which pollen enters

24.2. Flowers and Flowering

A. What is a Flower –structure used in the sexual reproduction of a plant. Major organs include:

1. The Structure of a Flower

a. ______– colorful, leaflike structures around the top of the flower stem.

b. ______– green, leaflike structures beneath the petals

c. ______– the male reproductive part

d. ______–produces pollen, found at tip of stamen

e. ______– female reproductive part

f. ______– a structure with one or more ovules, each containing one egg

2. Modifications in Flower Structure - Complete flowers have sepals, petals, stamens and a pistal. Incomplete flowers lack one or more organs.

B. Photoperiodism – Biologist used to think that the length of day controlled flowering, but now it is thought that the length of night controls flowering

1. ______– the response of flowering plants to the difference in the duration of light and dark periods. Controls flowering

a. Short-day plants - induced to flower by long nights (ex: pansies)

b. Long-day plants – induced to flower by long days (ex: lettuce)

c. Day-neutral plants – other factors control flowering (temp, moisture…most plants

24.3. The Life Cycle of a Flowering Plant

A. The Life Cycle of an Anthophyte – In anthophytes, the gametophyte generations is contained within the sporophyte, similar to conifers. Sporophyte stage is dominant (pg. 668)

1. Development of the female gametophyte- Female gametes develop in the ovule w/in ovary

a. Polar nuclei –

2. Development of the male gametophyte - Male gametes develop in the anther. Pollination occurs when a pollen grain fertilizes an egg (methods: wind, water, animal…)

3. Pollination – In anthophytes, pollination is the transfer of the pollen grain from the anther to the pistil. Wind pollinating plants produce massive amounts of pollen. Animal pollinating plants usually produce nectar. Bright flower color attracts pollinators.

4. Fertilization – Each pollen grain contains two haploid cells, the tube cell, and the generative cell. The tube cell winds to the ovary and connect to the micropyle. The generative cell divides into 2 sperm cells that make their way to the egg

a. Double fertilization - occurs when one sperm fertilizes the egg, and another sperm joins with the central cell. Then, the endosperm forms.

b. Endosperm – food storage tissue that supports development of the embryo in seeds.

B. Seeds and Fruit – The embryo contained within a seed is the next sporophyte generation.

1. Seed Formation - After fertilization, flower parts wither and die. The ovule wall becomes the hard seed coat

2. Fruit Formation - As the seeds develop, the ovary enlarges to become the fruit which protects and disperses the seeds

3. Seed dispersal – fruit not only protects the seed, but it also may aid in dispersal (ex: animal waste, clinging fruits, wind)

4. Seed germination -

a. Dormancy – a period of inactivity for seeds

b. Germination – the beginning of the development of the embryo into a new plant

c. Radicle – embryonic root (appears 1st)

d. Hypocotyl – portion of stem nearest the seed

5. Vegatative Reproduction – when new plants develop from roots, stems and leaves of certain plants.

a. Vegatative propagation – growing many plants from 1 plant (ex: potato tubers)