Overview

Frangipani_flowers.jpg
Frangiapani flowers

Angiosperms are plants that produce a variety of flowers, seeds and fruits. These flowering plants make up 90% of all modern species with 260 000 species spread around the world [1]. Most are terrestrial and lack locomotion [2]. They are descendants of Gymnosperms and have diverged around 245 - 220 million yearsago [1].

Characteristics


Unlike their ancestors, whose seeds are enclosed inside of a cone, Angiosperms have exposed sexual organs and seeds. Their reproductive organs include[1][2][3]:
flower%20parts.jpg
Parts of a typical flower

  • Stamens (male) - consists of the filamen (the stalk structure), and the anther (the tip that releases pollen grains)
  • Microspores - male gametophytes that develop into pollen grains.
  • Pistil (female) - consists of an ovary (the bottom end where the seeds are produced), a style (the stalk structure), and a stigma (the sticky part of the tip that traps pollen grains)
  • Megaspores - female gametophytes that develop into ovules in the ovary that are ready for fertilization.


Angiosperms can either be perfect (containing both stamens and pistils) or imperfect (containing either stamens or a pistil, but not both) [2][3]. They can be further classified as monoecious (has stamens and pistils, but separate and away from each other) and dioecious (separate plants that have stamens or pistils, but not on the same plant) [2]. Perfect flowers can also be monoecious.
boxelder%20flowers.jpg
The Boxelder is an example of an imperfect flower
Pink-Rose.jpg
The Rose is an example of a perfect flower

Life Cycle


In Angiosperms, male gametophytes divide their nucleus into two without splitting the cytoplasm [3]. One of the nuclei divides into two sperm nuclei while other nucleus become a tube nucleus, which will be responsible for transporting the sperm nuclei. Once the male gametophyte (the pollen grain) lands on the stigma of a nearby plant, the tube nucleus makes a tube running down the pistil into the ovary where sperm nuclei can germinate themselves into the ovary. Inside the ovary are the mature female gametophytes, which are called ovules. Upon entry of one, a sperm nuclei unites with an egg nucleus to form a 2n zygote, which then develops into an embryo. The other sperm cell unites with two other female gametophytes to make a 3n endosperm, which serves as a source of nutrition for the embryo. Once the triple fertilization occurs, the embryo becomes a seed and the endosperm becomes a fruit [2][3].

Fruits

The main role of fruits are for seed dispersal. They can do this in many ways[1][3]:

  • Wind (ex. dandelions)
  • Water (ex. coconuts. Once they fall off a tree, they are carried away to different locations on water)
  • Sticking onto animals (ex. burdocks)
  • Edible fruits. Animals eat fruits and bury their nuts, like squirrels.
  • Some fruits explode as they dry, expelling their seeds. (ex. wisteria)

Human Uses

Angioperms are the most popular type of plant used by humans [1][4]. They are commonly used for to diversify gardens and for gifts on special occasions such as Valentine's Day. Plants take in carbon dioxide in exchange for oxygen. Since they are
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A royal garden with a variety of flowers
the most populated around the world, they produce vast amounts of oxygen, which we need to breathe. The most important use is for food production. Not only do Angiosperms provide many fruits and vegetables for us they provide food for livestock aswell, which are also used for food production. Most importantly, they keep us with a steady and viable source of staple foods (easily farmed and maintained), including rice, wheat, barley and corn [1][4][5]. Many flowering plants have medicinal ingredients that benefit humans aswell [4]. They can also benefit our soil [5]. Many flowering plants form symbiotic relationships with fungi and bacteria that help condition and add nutrition to the sorrounding soil [5]. For example, Legumes hosts Rhizobia, which is a type of bacteria that fixes atmospheric nitrogen fo the host plant and the sorrounding plants to feed off of [5].

Quiz

  1. What does a perfect flower contain?
  2. Why is it advantageous for Coconut trees to grow by a creek?
  3. If a 3n cell has three set of chromosomes and a 2n cell has two sets, how much does an n cell have?
  4. What percentage of modern species do flowering plants make up?


Answers

  1. Stamens and pistils (male and female reproductive organs).
  2. When a coconut falls, it can be carried to a different location with the help of water.
  3. Half a set of chomosomes.
  4. 90%

References


1 – Dulson J, Fraser D, Vavitsas A, & Ledrew B Nelson Biology 11: University Preparation. Toronto: Nelson Education Ltd.; 2011.
2 – Unknown. Sexual Reproduction in Angiosperms. [homepage on the Internet]. 2010 [cited 2012 Jun 17]. Available from: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/Angiosperm.html
3 – Carter JS. Angiosperms. [homepage on the Internet]. 1997 [cited 2012 Jun 17]. Available from: http://biology.clc.uc.edu/courses/bio106/angio.htm
4 – Junkere B. Helium. [homepage on the Internet]. 2009 [cited 2012 Jun 17]. Available from: http://www.helium.com/items/1469876-angiosperms
5 – Belyeu S. Why Are Angiosperms Important? [homepage on the Internet]. 2009 [cited 2012 Jun 17]. Available from: http://www.ehow.com/about_6628704_flowering-plants-important-earth-humans_.html