Chapter 2 BOT3015L Introduction to Autotrophs and Osmotrophs Presentation created by Danielle Sherdan All photos from Raven et al. Biology of Plants except when otherwise noted Organisms able to synthesize nutritive substances required for growth (auto=self, troph=feed/grow) Organisms that take up nutritive substances required for growth by osmosis (osmo=take up from external, troph=feed/grow)

Today Plant cells –characteristics of plant cells –plastids –large central vacuoles –cell wall –effects of osmosis on plant cells –cell division

Microscopy enables the discovery of cells Slices of cork. Drawing by Robert Hooke, who coined the term “cell” in the 1600s Harvesting cork for commercial purposes

Modern cell theory The modern cell theory states that 1.All living organisms are composed of one or more cells 2. Chemical reactions of living organisms take place within cells 4. Cells arise from other cells 3. Cells contain the hereditary information of the organisms of which they are a part, and this information is passed from parent cell to daughter cell

Generalized diagram of a plant cell Note: As you will observed, much variation from this generalized diagram exists.

Cytoplasmic streaming of chloroplasts Considering their function, why would movement of chloroplasts by cytoplasmic streaming be advantageous?

Amyloplasts store starch Amyloplasts in a bean root Today, we will use staining techniques (iodine stains starch) to visualize amyloplasts in potato tubers

Observing the vacuole Put cells in a bath of concentrated solution What do you expect?

Osmosis

Plasmolysis --Low external solute concentration --High internal solute concentration, thus positive pressure inside. --Positive pressure in the plant cell pushes against the restricting cell wall, like a water balloon in a cage. Normal physiological conditions Under high external solute concentrations --External water potential decreases to below that inside the cell, thus osmotic water efflux from the cell. This process is plasmolysis.

Today Plant cells –characteristics of plant cells –plastids –large central vacuoles –cell wall –effects of osmosis on plant cells –cell division

Mitosis and cytokinesis

Mitosis (nuclear division) simplified diagram chromosome replication during S phase of cell cycle chromosomes condense and nuclear envelope degrades chromosomes align along metaphase plate and are attached to cytoskeleton chromosomes are pulled apart to opposite poles, notice both sets are identical nuclear envelope forms around each set of chromosomes Homologous chromosomes

Cell division in plants occurs at meristems Onion root meristem located at tip of root

Compare mitosis and meiosis

Total number of cell divisions? Fill in ploidy level in above “cells” Pairing of homologs? Crossing over?

Comparison chart II mitosis meiosis Centromeres divide? How many daughter cells are genetically identical to original cell?

or triploid or tetraploid… or tetraploid or hexaploid…, but not triploid, why?