Page 301 - ABCTE Study Guide_Neat

Seeds

Vascular plants are divided into seedless plants and seed plants. Seedless live close to water. Over time,
as plants developed farther away from water sources, they developed seeds. Seeds permit an embryo to
survive long periods of time in unfavorable conditions and to disperse an embryo from its parent plant.

Stems

Stems vary in size and shape from one plant species to another but all stems have two basic functions:
holding leaves up in the sunlight and conducting various substances between roots and leaves. In
addition, some stems store water and nutrients.

Leaves

The leaves of a plant are the world's most important manufacturers of food. Most leaves have a basic
structure of a large, flattened surface called the blade that is attached to the stem. Leaves are covered by
a layer of tough epidermal cells and a waxy cuticle. Most leaf tissue is composed of specialized cells
called mesophyll. This tissue contains chloroplasts and performs most of the plant's
photosynthesis. Some plants have modified leaves specialized for protection, water conservation,
climbing, and reproduction. Remember that most plant parts are basically modified leaves.

Many single-celled organisms use only anaerobic respiration, where carbohydrates such as glucose are
split apart and a small amount of ATP is released. Larger organisms, however, require more massive
inputs of ATP and depend on aerobic respiration and hence oxygen. Let’s look at the process in detail and
see where energy is put into and received from these three steps.

Aerobic Respiration

Step 1:

In the cytoplasm, glucose molecules are broken apart using the energy from two ATP molecules in the
process called glycolysis. Glycolysis releases four ATP for a net of two molecules.

Step 2:

In the second stage, the glucose molecule has been broken apart and has formed two pyruvate and two
NADH molecules. In the mitochondria of the cell, the Krebs Cycle converts the pyruvate into two ATP
and six NADH while releasing carbon dioxide. All of the NADH then is used in the third stage, the electron
transport stage.

Step 3:

The electron transport chain utilizes the oxygen we breath to act as an electron acceptor and drive the
production of thirty-two ATP molecules.

Here’s the important part: For a total investment of two ATP initially along with a supply of oxygen and
removal of carbon dioxide, our cells can produce a total of thirty-six ATP molecules to operate the various
processes inside the cell.