Biod Exp 6

Experiment 6: Gymnosperm and Angiosperm Gymnosperms Characteristics: 1. Do not produce flower or fruit. 2. Include plants with ovules not enclosed in carpel (naked seed). 3. Absence of companion cells in phloem. 4. Heterosporous, producing microspores that develop into pollen grains and megaspores that are retained in an ovule. 5. Fertilized by pollination through agents such as insects and wind. 6. Divided into four divisions: (i) Pinophyta (Pinus) (ii) Ginkgophyta (Ginkgo) (iii) Cycadophyta (Cycad) (iv) Gnetophyta (Gnetum, Ephedra, Welwitschia) 7. Cycads and Ginkgo have motile sperms that swim directly to the egg inside the ovule, whilst conifers and gnetophytes have sperms with no flagella. Their sperms reach the egg cell by a pollen tube that grows through ovule tissue. 8. Pine is the most commonly studied gymnosperm. In pine, the male cone has modified leaves called microsporophylls. Each microsporophyll bears a microsporangium within which the microspores are produced. The microspore divides and grows to form a fournucleus male gametophyte which is known as pollen. A grain of pine pollen has two large air sacs to make it buoyant in the wind. The female cone has scales called megasporophylls that produce megaspores. During pollination, a pollen tube will grow from the pollen to transport the sperm to the egg cell.

Figure 1: The male cone of pine

Figure 2: The female cone of pine

Angiosperms Characteristics: 1. Flowering plants. 2. Have closed carpel enclosing the ovule. 3. Presence of companion cells in phloem 4. Heterosporangous, which produce pollens in stamen and ovules in carpel. 5. Double fertilizations: one sperm cell fuses with the egg cell forming the diploid zygote (2n) whilst another fuses with the polar nuclei (mostly two) forming a triploid (3n) endosperm nucleus. After double fertilizations, each ovule develops into a seed. 6. Divided into two classes: (i) Magnoliopsida (Dicots) (ii) Liliopsida (Monocots) 7. Seeds with two cotyledons are called dicots (e.g., bean) whilst seeds contain only a single cotyledon are monocots (e.g., corn). 1

Figure 3: The structure of a flower.

Figure 4: The differences of a monocotyledon and a dicotyledon plants.

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