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index ad1861e..78866cd 100644
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+++ b/.obsidian/workspace.json
@@ -132,9 +132,23 @@
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+              "title": "Cell Size"
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@@ -318,8 +332,10 @@
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@@ -327,7 +343,6 @@
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diff --git a/biology/Cell Structure and Function/Cell Size.md b/biology/Cell Structure and Function/Cell Size.md
new file mode 100644
index 0000000..569b34a
--- /dev/null
+++ b/biology/Cell Structure and Function/Cell Size.md	
@@ -0,0 +1,30 @@
+[[Cell Structure and Function]]
+
+Surface area-to-volume ratio (SA:V) controls how well a cell exchanges materials and energy with its environment. Smaller cells have higher SA:V, so more efficient. As things get bigger, cells require more adaptations to remain fast.
+
+# Summary
+* Higher SA:V means more efficient exchange.
+* Volume grows faster than SA as a cell gets bigger, so SA:V decreases.
+* Folds and projections like microvilli and root hairs increase SA without adding much V.
+* Lower SA:V in larger bodies slows heat exchange and is linked to lower metabolic rate.
+
+Plasma membrane SA must be large enough to exchange stuff fast enough for cell needs. 
+SA:V doesn't only affect size, but also shape. Sphere isn't all that efficient for SA:V. 
+
+- _Sphere:_ SA = 4πr², V = (4/3)πr³
+- _Cube:_ SA = 6s², V = s³
+- _Cylinder:_ SA = 2πrh + 2πr², V = πr²h
+- _Rectangular Solid:_ SA = 2(lw + lh + wh), V = lwh
+
+Because SA:V impacts thermal energy transfer, larger organisms lose heat slower than smaller organisms proportionally.
+
+| Term                         | Definition                                                                                                                                                         |
+| ---------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
+| heat exchange                | The transfer of thermal energy between an organism's body and the surrounding environment; rate decreases as organism size increases.                              |
+| membrane folds               | Infoldings of the cell membrane that increase surface area to facilitate more efficient material exchange in complex cells.                                        |
+| metabolic rate               | The rate at which an organism uses energy; typically higher per unit body mass in smaller organisms than in larger organisms.                                      |
+| nutrient exchange            | The process by which cells obtain necessary nutrients from the environment.                                                                                        |
+| plasma membrane              | The selectively permeable membrane that surrounds the cell, composed of phospholipids, proteins, and other molecules that regulate what enters and exits the cell. |
+| surface area-to-volume ratio | The relationship between the total surface area and the total volume of a cell or organism; affects the efficiency of material exchange with the environment.      |
+| thermal energy exchange      | The transfer of heat energy between an organism and its environment.                                                                                               |
+| waste products               | Byproducts of cellular metabolism that must be eliminated from cells or organisms.                                                                                 |
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