Step 1: Understanding the technique
Tissue culture is a method of growing plants in a controlled environment using small pieces of plant tissue. It allows for the production of many plants from a single plant under sterile, infection-free conditions.
Step 2: Other options
- Spore association and binary fission are methods of reproduction for specific organisms (fungi and bacteria, respectively), not plants.
- Sexual reproduction involves the fusion of male and female gametes, leading to the formation of new plants.
Step 3: Conclusion
Thus, the technique used for producing many plants from a single plant is Tissue culture.
\[
\boxed{\text{Tissue culture}}
\]
$PQ$ is a chord of length $4\ \text{cm}$ of a circle of radius $2.5\ \text{cm}$. The tangents at $P$ and $Q$ intersect at a point $T$. Find the length of $TP$.