(CIE A2 Biology) Guard cells + stomatal openings/closures

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6 Terms

1
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the main features of guard cells

  • thicker stoma-facing cell walls + thinner adjacent epidermal cell-facing cell walls that’re plasmodesmata-free

  • cellulose microfibrils arranged around the cells in bands

  • folded plasma membranes w/ lots of channel/carrier proteins

  • high-chloroplast/mitochondria-density cytoplasm

  • lots of small vacuoles w/ fewer-grana thylakoids

  • lots of cristae in the mitochondria

<ul><li><p><strong>thicker stoma-facing cell walls</strong> + <strong>thinner adjacent epidermal cell-facing cell walls</strong> that’re <strong>plasmodesmata-free</strong></p></li><li><p><strong>cellulose microfibrils arranged around the cells in bands</strong></p></li><li><p><strong>folded plasma membranes</strong> w/<strong> lots of channel/carrier proteins</strong></p></li><li><p><strong>high-chloroplast/mitochondria-density cytoplasm</strong></p></li><li><p><strong>lots of small vacuoles</strong> w/ <strong>fewer-grana thylakoids</strong></p></li><li><p><strong>lots of cristae in the mitochondria</strong></p></li></ul><p></p>
2
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what happens when the guard cells become turgid

they open the stomata up

3
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how ATP-powered proton pumps respond to increased light intensity

by actively transporting H+ ions out of guard cells to make their insides more negatively charged than their outsides

<p>by <strong>actively transporting H<sup>+</sup> ions out of guard cells</strong> to <strong>make their insides more negatively charged than their outsides</strong></p>
4
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what happens after the guard cells’ insides become more negatively charged than the outsides

K+ channels in the guard cells’ plasma membranes open leading to K+ ions diffusing down an electrochemical gradient into these guard cells

<p><strong>K<sup>+</sup> channels in the guard cells’ plasma membranes open</strong> leading to<strong> K<sup>+ </sup>ions diffusing down an electrochemical gradient into these guard cells</strong></p>
5
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what happens after K+ ions’ diffusion into these guard cells

the resulting lower water potential leads to water diffusing through the guard cells’ aquaporins by osmosis (mostly entering the vacuoles thus leading to increased turgor pressure that opens the stomata up)

<p>the resulting <strong>lower water potential</strong> leads to <strong>water diffusing through the guard cells’ aquaporins by osmosis</strong> (<strong>mostly entering the vacuoles </strong>thus leading to <strong>increased turgor pressure that opens the stomata up</strong>)</p>
6
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what happens when the guard cells become flaccid

they shut the stomata up (in fact during stomatal closures everything happens opposite to what happens during stomatal apertures like reversed water potential gradients)