diff --git a/Grade 9/Science/SNC1DZ/Unit_3_Biology_Study_Sheet.md b/Grade 9/Science/SNC1DZ/Unit_3_Biology_Study_Sheet.md
index c109e62..f460f39 100644
--- a/Grade 9/Science/SNC1DZ/Unit_3_Biology_Study_Sheet.md	
+++ b/Grade 9/Science/SNC1DZ/Unit_3_Biology_Study_Sheet.md	
@@ -455,10 +455,16 @@ efficiency varies from `5%` to `20%` energy available between successive trophic
 - `Limiting factors` can be something such as access to water, availability of food. Can be **both** `abiotic` and `biotic`. Human influences often act as `limiting factors`. 
 - The carry capacity of an ecoystem is a limit where the organisms in that ecosystem can sustain themselves, human impacts often lower the `carry capacity`, as things such as pollution, destruction of habitats drastically lowers the `sustainability` of a ecosystem. In general, `limiting factors` link directly to `carrying capacity` as the the factors tell us the size that that the ecosystem can sustain itself. Which is essentially the `carrying capacity`.
 
+### Successions
+- **Primary Succession**: occurs on soil or bare rock, where no life previously existed, such as following a volcanic eruption
+- **Secondary Succession**: follows a disturbance that disrupts but does not destroy the community. The regrowth of an area following a forest fire is an example of secondary succession.
+- Succession provides a mechanism by which ecosystems maintain their long-term sustainability. It also allows ecosystems to recover from natural or human-caused disturbances.
+
 ### Argoecosystem v.s Natural
 - The natural ecosystem is more sustainable, as there is a abudance of biodiversity, unlike argoecosystem which are usually monocultured. Which is unsustainble.
 - We need both of these ecosystems, as we are in need of very fast supply of certain foods due to the vast demand of it.
-
+- Leaching happens in agroecosystems, where nitrogen rich water from fertilizers seep into the soil. This causes nutrients to dissolve in water and seep out of the soil. Increase growth of algae, (think eurotrophication).
+- 
 
 ### Ecosystem Services/Products
 - **Cultural Services**
@@ -480,10 +486,6 @@ efficiency varies from `5%` to `20%` energy available between successive trophic
 - Protect land from storms along coasts where wave damage erodes the shoreline.
     - Mangroves.
 
-
-### Engineered Ecosystems
-- Leaching happens in agroecosystems, where nitrogen rich water from fertilizers seep into the soil. This causes nutrients to dissolve in water and seep out of the soil. Increase growth of algae, (think eurotrophication).
-
 ### Pesticides
  - Pesticides can easily flow through food chains as there are not easily excreted, like DDT. There are fat-solutable.
  - DDT can be passed through organisms, from generation to generation, as the food we eat contains small amounts of DDT, and thus, the cycles continues. It doesn't matter how many generations ahead you are, everyone in the world contains some amount of DDT in their bodies.