Plants, like all living organisms, need both calories and vital nutrients. What is the difference? We get calories in the form of covalent bonds between atoms – it doesn’t particularly matter which atoms store the energy. In the case of minerals and nutrients, the specific atoms matter a great deal. Consider chlorophyll, a large molecule with a single atom of iron at its center. If a plant doesn’t get a minimal supply of iron, it will lack chlorophyll and therefore suffer from stunted growth. Plants require a number of nutrients, the main three being Nitrogen, Phosphorus, and Potassium. In smaller quantities, plants need the following: C HOPKINS CaFe (carbon, hydrogen, oxygen, phosphorus, potassium, iodine, nitrogen, sulfur, calcium, and iron).

Root: Plant tissue important for uptake and anchoring.

Starting from the inside, the following material can be found in a typical root: vascular cylinder, endodermis, casparian strip, exodermis.

The vascular bundle is made of xylem and phloem. In monocots, the tissue is organized into a vascular ring, while dicots display an "X" shape. This vacular tissue is surrounded by endodermis cells, which basically wrap the vascular tissue. If you look at a brick wall, the concrete between the bricks is known as mortar – if the cells making the endodermis are compared to bricks, the Casparian strip is the mortar, an impermeable barrier across which fluid can’t move? So how can it move in towards the vascular bundles? It must move through the cell membranes, thus the endodermis becomes a "filter" of sorts for the vascular tissue for the entire plant. (Recall: Large and/or charged molecules or atoms are unable to pass through a phospholipid bilayer.)

Monocot Dicot

Certain roots have special adaptations:

Root hairs are fine extensions that are often found in roots to increase surface area.

Root nodules are bumps in certain roots that are growths in which nitrogen-fixing bacteria grow.

Mycorrhizae are two symbionts: fungus and young roots.

Transpiration: Evaporation of water through the parts of a plant.

Xylem consists of straws (dead, lignin-reinforced cell walls) called tracheids. Thus dead cell walls can’t ‘pump’ or ‘push,’ so how does water get to the top of a tree such as a redwood? The answer is transpiration, explained by the tension-cohesion theory:

Tension-cohesion theory:

1. Pressure Difference. Low pressure outside of leaves is caused by the drying affect of air. In comparison, the roots have a high water pressure due to the protection from the dry air.

2. String of Water. Water molecules are cohesive, meaning they stick together (recall the Mickey Mouse molecule with positive ears and a negative face). They will also adhere to the trachied cells (think of the meniscus on the side of a test tube). The result is that water can form a continuous string within the lignin straw.

3. String is Pulled Up Plant. The low pressure in the leaves is enough to pull the string up the plant. If it weren’t for transpiration in the leaves, the plant would not be able to pull water up from the roots.

Role of Stomata: Only 2% of the water used by an average plant is used in photosynthesis. The rest is lost through the stomata (plural of stoma). The stomata are openings in leaves that allow plants to take in carbon dioxide but also allow water to escape. Each stoma is surrounded by two guard cells that can open and close. These guard cells are the only epidermal cells that have chloroplast. When conditions are right, the guard cells fill K+ ions and water immediately follows due to osmosis (this pressure is known as turgor pressure). When filled, the cells balloon up and open the stomal opening, allowing increased gas exchange. In certain plants (C4 or CAM plants), this is altered as they take in CO2 at night so they can close stomata during the day (cacti are an example). When no light is present, the K+ leave and the guard cells empty, closing the stomal opening.

Phloem: vascular cells responsible for moving the products of photosynthesis (sap). Phloem cells are made of parenchyma cells known as sieve cells. Along the side of a chain of sieve cells are companion cells, which actively load sugars into the companion cells. When the sugars are pumped into the sieve cells, water follows, creating osmotic tugor pressure within the column. Where will the sugar be used? At a sink (location where sugar pressure is reduced) such as a flower (nectar), growing portion of plant (meristem), or wound. The result is translocation, where the sap moves from high pressure to low pressure.