“The growth and development of a plant are influenced by genetic factors, external environmental factors, and chemical hormones inside the plant. Plants respond to many environmental factors such as light, gravity, water, inorganic nutrients, and temperature.” ~ Biology Online ~ Growth and Plant Hormones.
How does a seed ‘know’ when to germinate? How does a tree ‘know’ when to start changing leaf colour and drop it’s leaves for winter? How does a plant ‘know’ which direction to grow leaves and roots and where the light is? How does a plant ‘know’ when to produce flowers and what colour they should be? Instead of having a brain, central nervous system and endocrine system that co-ordinate communication, every plant cell can produce hormones (growth substances) that are transported throughout the plant via diffusion from cell to cell and through the xylem and phloem. (How mobile are plant hormones?).
Botanists recognize five major groups of hormones:
- abscisic acids
Although plants usually appear not to move, time-lapse photography shows that plants do, in fact, move and sometimes quite quickly. There are different types of movement, tropisms and nastic movements:
- geotropism (or gravitropism)
- thigmonastic movements
- seasonal responses
Draw up a table with three columns, with each of the key concepts above in the first column, a definition in the second column and an example in the third column. You can get your information from these resources:
Use digital tools to create a labelled image showing the different plant hormones, where they act (leaves, stems, roots, fruits, flowers etc) and what they do. Copy and paste a link to the image in the comment section below.
Over the semester break, please read through Chapter 10 carefully and start to answer the Chapter review questions. Leave a comment below or email me if you have any trouble with those questions. Physiological adaptations are ways that organisms are able to survive due to the way that they function. So succulent plants, such as those pictured above in Port Fairy, and mangroves are able to tolerate salty environments due to physiological features such as a thick cuticle that reduces water loss and salt glands that excrete excess salt.
Koalas have physiological adaptations that enable them to survive on a high fibre, low protein diet. As well as the obvious behavioural adaptations (usually slow moving and sleepy), koalas have reduced metabolic requirements and a slow metabolism, that enables them to survive on a diet of Eucalyptus leaves. Living organisms have evolved a great variety of strategies that enable them to survive extreme conditions in almost every place on the planet – temperature (hot and cold); moisture (wet and dry); chemical (high salinity for example); oxygen availability and fire tolerance. Some great examples at BBC Wildlife Finder – Adaptations.
This week we are starting the topic “Reproduction” by looking at vegetative or asexual methods of reproduction. Complete the table titled “Types of Vegetative Reproduction” using your text and activity manual. Plants that are produced by vegetative reproduction are genetically identical to their parent plants, which is a very useful trait for horticulturalists. They may use the following methods:
- Runners (strawberries, water hyacinth)
- Cuttings (geraniums, roses)
- Rhizomes (underground stems, as in ferns, irises, ginger and galangal)
- Tubers (potatoes0
- Bulbs (daffodils, tulips, onions)
- Suckers (undersground stems that arise a distance from the parent plant eg. elm trees and blackberries)
Lichens are extraordinary symbiotic organisms that survive where each of their composite species wouldn’t survive on their own. The dominant species is a fungus – a consumer or decomposer organism – that partners with algae or cyanobacteria (sometimes both). Most lichens grow very, very slowly – often less than a millimeter per year, and some lichens are thought to be among the oldest living things on Earth. This article has more information about lichens: Lichen biology
Another type of symbiosis has recently been discivered between cacti and bacteria, that enables the cactus to survive in some of the earth’s harshest environments. These cacti can colonise sheer rock faces due to the presence of bacteria that release rock-dissolving chemicals.
How cacti become rock busters
This photograph shows our geotropism experiment, in which we pinned germinating broad bean seeds onto plastic cards with different orientations. No matter which way the beans were orientated, they all showed root growth towards gravity and shoot growth in the opposite direction. They were kept in the dark, so light was not a stimulus. Three more jars were set up with beans that had root-tips removed, shoot-tips removed and both root and shoot-tips removed. We will check these results after the weekend, to determine if the plant root-tip and shoot-tip removal has an effect on growth. More information about plant chemicals (including hormones, alkaloids, flavanoids and tannins) here:
Growth and Plant Hormones from Biology On-line
Tannins and tannins.
The life cycle of a fern is beautiful and a little complex, but can be learnt with the aid of diagrams. The fern has two life stages – a tiny, haploid phase (the gametophyte – n) and a diploid phase (the sporophyte – 2n), which is the obvious and recognisable plant.
Diagram of the Life Cyle of a Fern and another diagram from David Nelson. Student tutorial about the fern life cycle. Fern life cycle clearly showing haploid and diploid phases.
Print out a Life cycle of a Fern diagram here: life-cycle-of-a-fern-diagram