Introduction to Plant Structure and Growth IB Topic 9.1

Starting Points Green plants are autotrophic Green plants show wide diversity: mosses (bryophytes), ferns (filicinophytes), conifers (coniferophytes), and flowering (angiosperms) Photosynthesis Green plants manufacture carbohydrates from CO2 and water; energy is the waste product Light dependent (grana) Light independent (stoma)

Plants Green plants (Plantae) make up one of the 5 kingdoms of living things Characteristics There is a wall around each cell; chief component is cellulose (polysaccharide, extremely tough and protective material) Chloroplasts (site of …?) Green plants evolved about 500 million years ago from aquatic, single celled algae (Chlorella). Today angiosperms are the most dominant terrestrial plants.

Plant Structure and Growth Whether wood or herbaceous (non- woody), plants consist of stem, leaves, and root

Stem The stem supports the leaves in the sunlight, and transports organic materials (such as sugar and amino acids), ions, and water between the roots and leaves. At the top of the stem is a terminal bud or terminal growing point In the axil of each leaf is an axillary bud New cells are produced at these growing points.

Leaf A leaf consists of a leaf blade connected to the stem by a leaf stalk. The leaf is an organ specialized for photosynthesis.

Root The root anchors the plant And is the site of absorption of water and ions from the soil.

The structure of the sunflower plant

Tissue Maps A tissue map (sometimes called a low- power diagram) is a drawing that records the relative positions of structures within an organ or organism. It does not show individual cells

The distribution of tissues in the stem of the sunflower

From the tissue map in figure 10.2, it can be seen that the stem is an organ surrounded or contained by a layer called the epidermis The epidermis contains: Vascular tissue (xylem for water transport and phloem for transport of organic solutes) Vascular tissue is in a discrete system of veins or vascular bundles In the stem, the vascular bundles are arranged in a ring, positioned towards the outside of the stem

The distribution of tissues in the leaf of the sunflower

Figure 10.3 is a tissue map showing the distribution of tissues in a leaf Like the stem, the leaf is contained by a single layer of cells, the epidermis, and also contains vascular tissue in a system of vascular bundles The vascular bundles in leaves are often referred to as veins The bulk of the leaf is taken up by a tissue called mesophyll The cells are supported by veins arranged in a branching network.