Roots+and+shoots+notes

= Plants Introduction =

Note: these are Mr. Dunbar's pre-lesson notes. They are somewhat different from the ones that you took in class.


 * Homework related to this note: **
 * 1) pp. 529-535, questions 1-4;
 * 2) pp. 536-540, questions 5-8, 11
 * 3) dig up a weed and examine the whole plant, root and shoot.

Intro
Plants grow and reproduce like every other living organism. They even reproduce sexually, just like most animals.


 * **ADVANTAGES** || **DRAWBACKS** ||
 * tough || cannot move ||
 * ability to regenerate (totipotency) || easy prey (food source) for animals ||
 * ability to produce glucose (a sugar) as a source of **energy** || cannot eat to get **energy*** ||


 * Note: when Venus fly traps "eat" insect they do not capture the insects for their energy but for their nitrogen (normally plants can get nitrogen by absorbing it through the roots but Venus fly traps live in environments where that is not possible).

Since plants have these drawbacks they were forced to evolve the above advantages. Plants have to be a lot "tougher" than animals because they cannot run away from danger or escape a bad situation like a drought. Consider animals like snails or turtles -- slow but with tough shells (example of convergent evolution between plants and certain types of animals).

Groups of plants
Note: this note will be expanded on in another lesson.

Plants can be grouped into various categories (called taxa). Starting from the "top" all plants can be grouped into the following groups (pl. taxa, s. taxon):

1. Vascular (tubes) vs. non-vascular (no tubes) Vascular broken down into...

2. Angiosperms (flowering plants) vs. gymnosperms (confirs, etc.) Angiosperms broken down into...

3. Monocots (e.g. grass/wheat/bamboo, orchids) vs. dicots (e.g. dandelions, apples/roses) "Little white lie". Many people talk about monocots vs. dicots as if they were two distinct groups. However, the real story is more murky than that. Evolutionarily monocots are actually a subset of dicots. What this means is that the entire group of monocots are descended from a dicot ancestor that had dicot characteristics. The monocots lost some of the features of that the rest of the dicots inherited (e.g. monocots lost one of the seed leaves) and gained new ones as well (through evolutionary processes).

What is the primary feature that distinguishes monocot from dicots? cot = cotyledon which is a type of leaf
 * structure of seed

In the seeds of monocots there is only **one** seed leaf. In the seeds of dicots there are **two** seed leaves.

Other differences?
 * root and stem structure - tubes (vascular tissue) that carry water and food are laid out differently
 * structure of flowers (number of petals; 3 = monocot; 4 or 5 = dicot)
 * "real" trees can only be dicots. Palms are not real trees.
 * leaf structure (veins)

Modular nature of plants
Plants are "modular".

Plants are composed of a bunch of subunits. Leaves and flowers are essentially the same thing. The genes controlling both leaves and flower petals are very similar. What probably has happened is that a group of genes for leaves were duplicated at some point during a plant species' evolutionary history and were able to evolve into petals.

Basic structures are often duplicated or modified to grow or do something new. e.g. leaves -- they can be used to photosynthesisze but, the same basic idea can be used to produce flowers roots or stems -- normally they act as structural support or a place to absorb water and minerals but they can also be modified to store water or food energy.

=Roots & Shoots= Most plants are organized into two sections, roots and shoots.

Roots are found above ground, shoots are found below ground.

Roots
Tap roots vs. fibrous roots tap root = one big root plus lots of little ones branching off (e.g. dandelion) fibrous root = no central root (e.g. grass)

Function of roots...
 * 1) **anchor** plants to soil/rocks/other plants/etc.
 * 2) **absorb** water and minerals from surrounding soil
 * 3) **transport** water and minerals to stem for distribution to rest of plant
 * 4) **store** food or water for plant

Shoots
Contain the leaves and stems 1) **leaves** 2) **stem**
 * the primary site of **photosynthesis** (convert sun's energy into stored chemical energy)
 * sometimes store water and/or food
 * support leaves and flowers
 * transport water and minerals to leaves
 * transport food (sugars) to roots and other parts of the plant for storage and **cellular respiration**
 * sometimes store food or water
 * sometimes primary site for photosynthesis if leaves are small or thorn-like like in cacti (cacti are mostly giant stems, the leaves have been reduced to thorns that protect the plant)