<< Chapter < Page Chapter >> Page >

Leaf form

Leaves may be simple or compound ( [link] ). In a simple leaf    , the blade is either completely undivided—as in the banana leaf—or it has lobes, but the separation does not reach the midrib, as in the maple leaf. In a compound leaf    , the leaf blade is completely divided, forming leaflets, as in the locust tree. Each leaflet may have its own stalk, but is attached to the rachis. A palmately compound leaf    resembles the palm of a hand, with leaflets radiating outwards from one point Examples include the leaves of poison ivy, the buckeye tree, or the familiar houseplant Schefflera sp. (common name “umbrella plant”). Pinnately compound leaves take their name from their feather-like appearance; the leaflets are arranged along the midrib, as in rose leaves ( Rosa sp.), or the leaves of hickory, pecan, ash, or walnut trees.

Photo (a) shows the large-leaves of a potted banana plant growing from a single stem; (b) shows a horse chestnut plant, which has five leaves radiating from the petiole as fingers radiate from the palm of a hand; (c) shows a scrub hickory plant with feather-shaped leaves opposing each other along the stem, and a single leaf at the end of the stem. (d) shows a honey locust with five pairs of stem-like veins connected to the midrib. Tiny leaflets grow from the veins.
Leaves may be simple or compound. In simple leaves, the lamina is continuous. The (a) banana plant ( Musa sp.) has simple leaves. In compound leaves, the lamina is separated into leaflets. Compound leaves may be palmate or pinnate. In (b) palmately compound leaves, such as those of the horse chestnut ( Aesculus hippocastanum ), the leaflets branch from the petiole. In (c) pinnately compound leaves, the leaflets branch from the midrib, as on a scrub hickory ( Carya floridana ). The (d) honey locust has double compound leaves, in which leaflets branch from the veins. (credit a: modification of work by "BazzaDaRambler"/Flickr; credit b: modification of work by Roberto Verzo; credit c: modification of work by Eric Dion; credit d: modification of work by Valerie Lykes)

Leaf structure and function

The outermost layer of the leaf is the epidermis; it is present on both sides of the leaf and is called the upper and lower epidermis, respectively. Botanists call the upper side the adaxial surface (or adaxis) and the lower side the abaxial surface (or abaxis). The epidermis helps in the regulation of gas exchange. It contains stomata ( [link] ): openings through which the exchange of gases takes place. Two guard cells surround each stoma, regulating its opening and closing.

Photo (a) shows small oval-like stomata scattered on the bumpy surface of a leaf that is magnified 500 times; (b) is a close-up of a stoma showing the thick lip-like guard cells either side of an opening. Photo (a) and (b) are scanning electron micrographs. Photo (c) is a light micrograph of a leaf cross section that shows a large air space underneath two guard cells. The air space is surrounded by large oval and egg-shaped cells.
Visualized at 500x with a scanning electron microscope, several stomata are clearly visible on (a) the surface of this sumac ( Rhus glabra ) leaf. At 5,000x magnification, the guard cells of (b) a single stoma from lyre-leaved sand cress ( Arabidopsis lyrata) have the appearance of lips that surround the opening. In this (c) light micrograph cross-section of an A. lyrata leaf, the guard cell pair is visible along with the large, sub-stomatal air space in the leaf. (credit: modification of work by Robert R. Wise; part c scale-bar data from Matt Russell)

The epidermis is usually one cell layer thick; however, in plants that grow in very hot or very cold conditions, the epidermis may be several layers thick to protect against excessive water loss from transpiration. A waxy layer known as the cuticle    covers the leaves of all plant species. The cuticle reduces the rate of water loss from the leaf surface. Other leaves may have small hairs (trichomes) on the leaf surface. Trichomes help to deter herbivory by restricting insect movements, or by storing toxic or bad-tasting compounds; they can also reduce the rate of transpiration by blocking air flow across the leaf surface ( [link] ).

Questions & Answers

A plant is a living thing that grows in the earth and has a stem, leaves, and roots
Bello Reply
what is a plant
dalitso Reply
A plant is a living thing that grows in the earth and has a stem, leaves, and roots
a plant is an is a living thing that is classified under autothrops because it makes its own food through the process of photosynthesis .
what is plant
Odion Reply
Plants are autotrophic
Then animal are heterotrophic
what are organisms
Godfred Reply
the diagram below show how the blood of a human embryo flows close to the mothers blood in the placenta . which substances are represent at x in higher concentrations than at y
Joyce Reply
what is ecology
Odion Reply
what is cell
what is cell
What is a cell
Awal Reply
What are tissues
A cell is the smallest unit of living organisms.
Tissues are group of similar cells performing a particular function.
how to pronounce the word cyanobacteria
siva Reply
Cyano then bacteria. look that "cyano" is just like "ciyano".
explain the term transpiration pull
Tank Reply
water is mainly " pulled" through the plant and that the driving force for this process is transpiration from the leaves .This is also referred to as the cohesion- tension -transpiration pull model transport.
what Is corona
My brother go and ask GOOGLE😷😷😷
Google it for the right answer. Corona is a virus which causes Novel Covid-19 disease that has been declared by WHO as a global or world pandemic.
Why is it called Covid-19?
jjwhat is. condinative system
condinative system is the system that harmonize all the. different. part. of. the. body and make. them function as a. specific unit
Describe the process of protein sythesis?
Kizito Reply
Ribosomes are responsible for protein synthesis in animals.
What is a ploidy level
Francis Reply
Ploidy refers to the number of chromosomes. We have 23 pairs of chromosomes in somatic cells. Sex cells are haploid thus 23 chromosomes vs. 46 Chromosomes.
Evolution is evolvement according to one's environment. Let's use humidity as an example. A person from a very cold environment would not be used to hot humid weather. But over time their body would slowly, slowly adapt.
Give me (3) types of biodiversity
Hi guys 🇧🇪
hello boy
what do you guys understand about evolution?
Kiana Reply
it's a process or analayzing some program
but am not sure if some know plz let share
is a study of
unfolding or unrolling hence the process of development of growth
is the periodic change of the structural features of an organism
I think
process of developing
hi guiz
hello guys
Evolution ~ Is the gradual change of development over time in which a new species are formed
Evolution is the sum total of adaptive changes that has existed before.
why are diagrams not available
Evans Reply
How can nucleotide molecules of DNA be constructed?construct a six molecules of DNA?
Julia Reply
You take a Deoxyribose sugar. The Deoxyribose sugar has a hydrogen on the second carbon vs. an OH group. The nitrogenous base binds to the #1 Carbon and a phosphate binds to the 5'. When the 2nd NBase bonds, it does so on the 3' Carbon. Thus you have 5' to 3' directional growth.
what is the explanation of local biomes in Nigeria
It would be savanna, tropical grassland.

Get the best Biology course in your pocket!

Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?