Higher Plants Midterm I

Because oxygen, carbon dioxide, and minerals are generally more abundant on land than in water, terrestrial plants have greater access to these substances for growth and development. Water is often in short supply on land, however, and thus terrestrial plants have a much greater risk of drying out than do aquatic plants.

1)Water loss – cuticle formation (hydrophobic layer) on leaf surface 2) CO2 Uptake Limitations – opening/closing of stomatas so plant can deter substantial water loss yet still be accessible for gas exchange. 3) Structural support – vessels, tracheids, and fibers providing plant with structural support 4) Sexual reproduction + gamete drying – male reproductive organ produces pollen which has the ability to disperse in wind 5) Embryo protection – plants have seeds for protecting embryo from desiccation

In contrast to animal cells, plant cells have vacuoles, cell walls, and plastids.

Vacuoles store primary metabolites, reserve proteins, and anthocyanins. In addition, vacuoles are involved in the breakdown of organelles and macromolecules, thus facilitating the recycling of chemical elements within the cell.

1. Sequester toxins
2. May contain enzymes (cyanide poisoning via cyanogenic glucosides)
3. May contain calcium salts
4. Store or take up water for cell growth and expansion.

The membrane that surrounds the vacuole is called the tonoplast. The tonoplast separates the vacuole contents from the cytoplasm.

The chloroplasts of photosynthesizing eukaryotes are thought to have originated in the endosymbiosis (engulfment of a bacterium by another free-living organism) of a cyanobacterium.

Sea slugs are photosynthetic animals who feed on algae (environment) and store chloroplasts inside their bodies. In eukaryotic photosynthetic cell (plant cell) needs genes in their nucleus to keep chloroplasts alive. Just like plant, sea slugs can maintain chloroplasts within them for about 9 months. This must mean that the sea slugs have acquired the genes (most likely from the algae) to keep their acquired chloroplasts alive.

A membrane bound organelle whose functions are largely dependent on the pigments they contain. The three main classes of plastids are: Leucoplasts (white), Chloroplasts (green), and Chromoplasts (red/orange)

Leucoplasts (White Plastids) -Proplastid - not fully developed (white/colorless) -Amyloplast - primary function to store starch (white/colorless) -Etioplast - initially white and colorless; develops in the dark and will become a chloroplast upon exposure to light. The internal membrane structure consists of a lattice structure of tubules called a prolamellar body. Chloroplasts - green - photosynthesis Chromoplasts - orange/red - depending on the tissue, may attract seed dispersers, pollinators. The red/orange color will make plant attractive.

Plastids will degrade and subsequently chloroplasts will disappear. Carotenoid synthesis may occur in conversion of a chloroplast -> chromoplast [you get some sort of a crystal or fibrillar association with oil in chromoplast] **a chromoplast isn’t necessarily created only from chloroplasts

Light interaction with plant via photosynthesis will produce the green pigment chlorophyll which will give a pale plant its green color upon exposure to light. Essentially chloroplast activity is turned on in light. A green fruit turns red as it matures due to the decreased chloroplast activity, thus enhancing the the chromoplasts present.

-Microfibrils of cellulose (polymers of glucose). The microfibrils are several chains of cellulose twisted together. -Cross-linked by some proteins and hemicellulose which is a type of branched carbohydrate. -Pectin (hydrophobic) inserted between microfibrils of cellulose and also makes the middle lamella. Pectin is hydrophillic; this is extremely important as it holds water in the cell wall and allows therefore for enzymatic reactions to occur which can pave way for cell expansion. It also allows moleules to diffuse through the cell wall.

They have an additional 3 layers of cellulose and are often lignified. Cells with secondary cell walls often put lignin in the cell walls. Lignin is hydrophobic. It does crosslink cellulose to make it structurally strong. Lignin displaces pectin; no water in the cell wall means no further expansion, division, etc. 3 layers of cellulose in a secondary cell wall are laid down in different orientation. One layer is in opposing orientation to the other; this provides with great strength.

Primary pit field will have groups of plasmadesmata. Secondary cell walls will not be deposited on the primary pit fields. Remember secondary cell walls have 3 layers associated with them; therefore, in places where the secondary cell wall is not deposited to make way for primary fit fields, that area is known as the pit. The pit membrane is made of primary cell wall. Essentially a meshwork of cellulose (water can diffuse through the pit membranes as they are remnants of the primary cell wall).

Primary growth is produced by the apical meristems. All plants undergo primary growth & contain apical meristems. They will be found at the tip of the shoots and roots. Meristematic cells have small vacuoles, weak cell wall, big nuclei, densely cytoplasmic. Their sole function is to divide and provide new cells.