Biology Notes - Plant Science

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Topic 9 – Plant Science
First lesson
Without photosynthesis there would be no life.
Important words:
Plants have groups of stemcells that live throughout their lives = meristem. Tissue – Many cells of the same type working together.
Organ – Two or more tissues working together with the same task. Organ system – Several organs working together with a common task. Angiospermophytes
Angio – container
Sperma – seed
Phytes – plant
= Plants producing seeds enclosed in a fruit
Can be divided into two groups
Monocotyledons/monocots
Have on leaf when they germinate.
Dicotyledons/dicots
Have two leaves when they germinate.
Cotyledon – Leaf formed in the embryo. The first leaves that appear when germinating. {draw:frame}
Monocots
Grasses, bananas, palm trees, gingers, lilies, irises, sedges. Most woody plants and shrubs, many non-woody plants
The leaf of a dicot
{draw:frame}
Plan diagram – Shows distribution of tissues, no individual cells. 27/08/09
Three tissues in leaf
Mesophyll tissue
Epidermal tissue
Vascular tissue
Filling out most space in the leaf
Have chloroplasts
Two major types
The two main types of mesophyll
Palisade mesophyll
Spongy mesophyll
Palisade mesophyll
1-2 layers of regular “stacks”/tiers
Many chloroplasts, since they are close to the leafs surface ? highest light intensity. Spongy mesophyll
Irregular (placed very randomly)
Fewer chloroplasts
Air spaces in-between the cells ? gas exchange efficient within the leaf Epidermis
Single cell layer covering the surface
Transparent, no chloroplasts
Waxy layer ? thick on upper epidermis, thin on lower epidermis Protects against transpiration and some insects
In the lower epidermis there is stomata
Consists of two guard cells that form a pore that can open and close Regulate gas exchange (CO2, O2, H2O 8g9)
Guard cells have chloroplasts
Vascular tissue
Has xylem (water and ion transport to leaves)
Long dead, tubular structure
Also has phloem (transports products of photosynthesis e.g. amino acids and sugah to roots and storage places Lines of living cells with pores between the cells.
Xylem and phloem form vascular bundles = veins
Veins form a network that support the leaf structure
The stem (of dicots)
Transport materials (water, sugar, minerals etc.) between leaves and roots Support the leaves ? get as much light as possible
Consists of either or both collenchymas and parenchyma cells and some fibres. Distribution depends on the age of the stem. Young stems (makes the bendy)
Highly flexible
Living cells
Small regular shape
Parenchyma (cells)
Support herbatious (when they don’t have wood (fibres), no bark etc) when turgid Starch storage
Consist of living cells
Large cells, sometimes with airspace inbetween
Pith
Consists of parenchyma cells
Old stems are sometimes hollow in the middle
Small vascular bundles
Traces of bundles to, old leaves that have fallen off Fibres Old cells that died/remains of old cells
Cellulose and lignin in cell walls
Support the stem
Plant growth
Plants grow on shoot and root tips in meristems
Dicots also have lateral meristem
Apical meristem = in the shoot tip
As stems grow upwards leaves and branches are formed, the lower parts of the stem has to support larger and larger mass. Three ways that make it possible for the stem to support the mass Fibres made of cellulose and lignin in dead cells.

Turgid cells (parenchyma cells) become totally rigid
Living cells with a thick cell wall of cellulose and lignin PLANTS CAN MOVE!!
Phototropism...
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