Summary
Pores on leaves flanked by guard cells that open and close to regulate gas exchange and water loss.
In depth
Guard cells swell with potassium and water uptake (turgid) to open the pore; light and low CO2 promote opening, and abscisic acid triggers closure in drought. Stomata balance CO2 uptake against water loss. Density varies with species and environment.
Opening is driven by blue light, low internal CO2 and proton pump activation, causing K+ uptake. Closing involves ABA signalling and anion release. Stomata are mostly on the lower leaf surface to reduce water loss.
Example: waterlilies have stomata on the upper surface of floating leaves.
A stoma is a pore with two guard cells, found mostly on the lower leaf surface; density varies from about 50 to 500 per square mm, and fossil leaf stomata are used to infer past CO2 levels (higher CO2 means fewer stomata). Opening is triggered by blue light through phototropin, which activates proton pumps, K+ uptake and malate accumulation, water enters by osmosis, and thick inner walls cause guard cells to bow outward.
Closing is signalled by abscisic acid under water stress, which causes K+ and anion efflux. Stomata balance CO2 gain against water loss and are therefore central to water-use efficiency. They also act as entry points for pathogens, and some close to block bacterial entry. CAM plants open them at night.
Example: ozone and drought can reduce stomatal conductance and crop yields.
Frequently asked questions
What is Stomata?
Pores on leaves flanked by guard cells that open and close to regulate gas exchange and water loss.
Which area of biology covers Stomata, and how advanced is it?
Stomata is one of the 56 topics in Plant Biology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Abscisic Acid and Drought, Transpiration, Plant Defence Responses.
Can you give an example of Stomata?
Many desert plants open stomata at night.
What should I learn before Stomata?
Stomata is a Beginner topic, so no earlier topic is required. Other Beginner topics in Plant Biology that pair well with it include Plant Kingdom, Photosynthesis, Chlorophyll.
What topics are related to Stomata?
The closest topics to Stomata are Abscisic Acid and Drought, Transpiration, Plant Defence Responses, Leaves. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Stomata?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Stomata. To practise the whole of Plant Biology, use the Plant Biology quiz.
How is Stomata different from Abscisic Acid and Drought?
Stomata: Pores on leaves flanked by guard cells that open and close to regulate gas exchange and water loss. Abscisic Acid and Drought: ABA triggers guard cell closure and gene responses that help plants survive water stress. Read both side by side and note what each one explains.
How should I study Stomata step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Abscisic Acid and Drought and explain the difference aloud. Finally, take the Plant Biology quiz and come back to this page for any question you miss.