S173 Plants and People - Notes from Study Period 2 - Part 1 of 2

In chapter two, we study what is probably the most obvious and well known use of plants - that of plants as a food crop. It's a good chapter with lots of great information, for that reason I'm splitting my notes into two posts. The first will deal with the topics associated with the botanical illustrations and the second will be notes of the other topics covered. That means I'm giving you the good stuff first - my awesome attempts at drawing!

Firstly we need to look at how new plants are formed. There are two main processes, pollination and fertilisation.

Pollination occurs by various means, such as by wind or by insects or other animals. But however pollination happens, it generally requires the same things; for the pollen to be delivered from the anther to the stigma. Normally that is, the pollen must travel from the anther on one plant to the stigma on another plant of the same, or similar species.
A flower generally has the parts of both the 'female' and the 'male', the process goes deeper than this with regard to the alternation of generations, but this is beyond the scope of the course.

A basic illustration of the flower is shown below:

After successful pollination, fertilisation can occur. The pollen grain absorbs moisture and the pollen tube, see below, emerges through a pore. One sperm fuses with the egg cell, which becomes the plant embryo, with the ovule becoming the seed. The other sperm fuses with a polar cell forming the endosperm. This double fertilisation is characteristic of angiosperms. If the pericarp remains with the fertilised seed, then it is known as a fruit.

The fruit comprises of three layers:

1. the outside skin
2. the tissue that is fleshy
3. the tissues which surround the seed

The process of fertilisation is shown below:

Then we need to look at what seeds actually are. In general terms they are packages that enclose a dormant embryo, that is awaiting favourable conditions for growth; and an energy source, in the form of starch, oil, and proteins, which will be immediately available to the embryo to support it until it can photosynthesise. Cotyledons are leafs and seeds fall into two categories (there is a third - the magnoliids, but this is beyond the scope of this course), the monocots - one leaf and the eudicots - two leaves. This energy source is stored inside the cotyledons for eudicots and is separate from the cotyledons in monocots.

The eudicot, is shown below and are characterised by having seedlings with two leaves, as seen in the photo.

The monocots generally have long thin leaves and parallel veins, such as grasses and cereals. Here is a photo of a grass to the left and an illustration of the monocot seed to the right.

Examples of different types of seed are:

• A single seed or stone: Plums, peaches 
• Several small seeds at the centre of the fruit: Apples, pears 
• Fruit that has an outer skin surrounding flesh that contains small seeds: Blackcurrants, tomatoes Citrus fruits: oranges, lemons 
• Fruits that have the seeds on the outside skin: strawberries

Well, that's it for part one. I'll link it to part two once I've written that up. If you have any comments, or any corrections that I need to make - please let me know!
Part 2 link.