Science Focus Topic 2 Notes: Structure and Adaptations
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Plants have particular habitats, each with its own set of environmental characteristics, including light, temperature water and soil conditions. The structure of a plant helps it to adapt to these conditions.
There is much more to a plant than what you are able to see above the surface of the soil. In fact, up to one third of the plant can be beneath the soil. Types of Roots
Roots perform several functions:
- they absorb water and minerals from the soil
- they support and anchor the plant so it cannot be relocated easily
- they store food to help the plant survive during times of scarcity
The most prominent part of the root in many plants is the taproot, with many smaller roots coming out from it, like branches on a tree. These smaller roots are covered in root hairs. The smaller roots and root hairs absorb water and nutrients from the soil.
Other plants have fibrous roots, which is a shallow system of similar-sized roots that can quickly soak up moisture.
Roots are often especially adapted to a plant's habitat.
Moss campion is an example of how a plant grows its taproot system throughout the early years of the plant's life, so that it can have a well established taproot system before the upper part of the plant matures (it can take up to 25 years for the plant to bloom).
The duckweed on the other hand has tiny roots on the underside of the leaf and are surrounded entirely by water.
Generally grow in a short period of time, usually survive when there is little moisture and can be stored for long periods of time
Diffusion and Osmosis (p. 107)
Diffusion is the tendancy of particles in a gas or liquid to become evenly distributed by moving from areas of greater concentration to areas of lesser concentration. The particles continue to spread out until they are evenly distributed within the enclosed area.
Osmosis is a particular type of diffusion in which only some of the particles are allowed to pass through a barrier. This barrier is called a differentially permeable membrane. Osmosis is the diffusion of water through a differentially permeable membrane.
One function of the stem is to transport water and nutrients between the leaves and the roots.
Another function of the stem is to support the leaves and to ensure that the leaves receive adequate light. To achieve this most stems grow above the ground
Another function of the stem is to store food for the plant. The food produced in the leaves is stored ion the stem - like potatoes, which have swollen underground stems called tubers (the starch they store is used by the plant to grow). Some plants store food as sugar as well - the sugar cane is a good example.
Different Types of Stems
Cattails Horizontal Rhizomes
Cacti Fattened Stems
|A pigment called chlorophyll makes the leaves green. The energy of the sun is trapped in the leaves and changed into a kind of chemical energy. Carbon dioxide and water are used by the leaves in the process called photosynthesis, to make sugar and give off oxygen. Plants also need oxygen - at night when photosynthesis does not happen, respiration does. Respiration is a process by which plants release carbon dioxide and let oxygen into their cells. Water enters and leaves the cells in the leaves through the guard cells. When they absorb water they swell, opening the stoma (which lets in carbon dioxide and lets out water vapor). The loss of water through evaporation is called transpiration.|
Moving Water in Plants
The pushing and pulling action of osmosis (pushing water up from the roots) and transpiration (pulling the water up the xylem tissue from the roots) moves water up to the very top of the plant.
Topic 2 Review p. 114