Update Study_Sheet.md

Grade 9/Science/SNC1DZ/Study_Sheet.md

@@ -524,6 +524,26 @@ atmosphere, river to lake)
 - Not all disturbances can be repaired.
 - Disturbances can be repaired through humans actions that support the natural processes of succession.
 
+## ECOLOGICAL BALANCE
+- `Population`: A group of organisms of one species that interbreed and live in the same place and time.
+    - Population often change due to both **natural and artifical** factors (human activity). 
+- `Carry Capcity`: The maximum population size of a **particular species** that a given ecosystem can sustain.
+
+## Changes In Population
+- The carry capcacity of an ecosystem depends on numerous biotic and abiotic factors.
+- These can be classified into two categories.
+    1. `Density dependent factors`
+    2. `Density independent factors`
+
+## Density Independent Factors
+- DIF’s can affect a population no matter what its density is. The effect of the factor (such as weather) on the size of the population **does not** depend on the **original size** of the population.
+- Examples:
+    - unusual weather
+    - natural disasters
+    - seasonal cycles
+    - certain human activities—such as damming rivers and clear-cutting forests
+
+
 ## Biodiversity
 - The variety